Sunspots, vortices of gas associated with strong electromagnetic

Hi

(A) are visible as dark spots on the surface of the Sun but have never been sighted on
Correct

(B) are visible as dark spots that never have been sighted on the surface of the Sun
darkspots
That modifies dark spots which changes the intended meaning

(C) appear on the surface of the Sun as dark spots although never sighted at
although begins a subordinate clause without a subject, thus making it a fragment

(D) appear as dark spots on the surface of the Sun, although never having been sighted at
although begins a subordinate clause without a subject, thus making it a fragment

(E) appear as dark spots on the Sun's surface, which have never been sighted on
which modifies surface and that makes no sense

1. I don't understand the OE of option (C), in that "sighted is not a complete verb".

The terms you and Tarek99 are looking for are Transitive and Intransitive verbs. Transitive Verbs require a direct object, whereas Intransitive verbs do not take a direct object (Instransitive verbs cannot be put in the passive voice).

So to answer your question directly, "to sight" is a transitive verb and requires a direct object; however if it is used as a noun modifier, then it does not require a a direct object since its not acting as a verb.

2. I don't understand the OE of the top paragraph which states "The adjective visible is a complement and is parallel to the past particle sighted"

Verbs in the past participle form can be used a noun modifiers. In general adjectives, Past Participles, and Present Participles (acting as a noun modifier) are all be parallel.

Take Care

Hello Everyone!

Let's take a closer look at this question, one issue at a time, and narrow it down to the correct choice! Before we dive in, here is the original question, with any major differences between each option highlighted in orange:

Sunspots, vortices of gas associated with strong electromagnetic activity, are visible as dark spots on the surface of the Sun but have never been sighted on the Sun’s poles or equator.

(A) are visible as dark spots on the surface of the Sun but have never been sighted on
(B) are visible as dark spots that never have been sighted on the surface of the Sun
(C) appear on the surface of the Sun as dark spots although never sighted at
(D) appear as dark spots on the surface of the Sun, although never having been sighted at
(E) appear as dark spots on the Sun's surface, which have never been sighted on

After a quick glance over the options, a couple major differences jump out:

1. How they begin: visible as / appear as
2. Verb tense: have been sighted / sighted / having been sighted

It's always a good idea to start with any issue that will eliminate 2-3 options at once. Let's start with #1 on our list because it'll eliminate the most options to get us started!

While it may seem that appear and visible are interchangeable terms, they do mean slightly different things:

Visible = The object already exists, is not moving, and you are able to see it. (The stop sign is visible from a distance of 200 yards.)
Appear = The object is created as you're looking, or it moves into your path of vision. (My dog appears at my feet when he's ready to go for a walk.)

It makes more sense in this context to say that sunspots are visible on the surface of the Sun. They already exist, and they aren't moving into your vision path - they are stationary. The sentence is merely stating that you are able to see them, not that they move around or are created in front of your very eyes.

Therefore, we can eliminate options C, D, and E because they use the more vague "appear," rather than the clearer term "visible."

Now that we have it narrowed down to only 2 options, let's take a closer look at the remaining options:

(A) are visible as dark spots on the surface of the Sun but have never been sighted on

This option is CORRECT! It uses the clear term "visible" to describe sunspots, and it makes logical sense to use "have never been sighted" to refer only to the poles and equator.

(B) are visible as dark spots that never have been sighted on the surface of the Sun

This is INCORRECT because it drastically changes the original meaning of the sentence! The original sentence states that we can see sunspots on the surface of the Sun, with the exception of the poles and equator. This sentence says they have never been sighted on the surface, which isn't true!


There you go - option A is the correct choice! It uses clear terminology and makes logical sense!

**************************************************************************************************************

Now, I'm sure you're wondering what would happen if we tackled #2 on the list instead. Here is how we could break down this question based on verb tenses:


(A) are visible as dark spots on the surface of the Sun but have never been sighted on

This is CORRECT because it uses the correct verb tense (present perfect) to show that they weren't found in the past, and haven't been found in the present too.

(B) are visible as dark spots that never have been sighted on the surface of the Sun

While this sentence uses the correct verb tense, the location of the verb is wrong! In this case, it's referring to the surface of the Sun, which doesn't make sense - we CAN see sunspots on the surface! This is INCORRECT because it drastically changes the intended meaning, which is a big no-no on the GMAT!

(C) appear on the surface of the Sun as dark spots although never sighted at

This is INCORRECT because it uses past tense to show that the sunspots were not visible in the past, but says nothing about the present. The original sentence suggests that the sunspots are still not visible on the poles or equator today, so we need to use present perfect tense to show that.

(D) appear as dark spots on the surface of the Sun, although never having been sighted at

This option is INCORRECT for a couple reasons. First, it doesn't make sense to say that sunspots aren't visible AT the poles or equator - it's clearer to say they aren't visible ON those areas. Second, it uses the wrong verb tense (past perfect) in passive voice, which changes the meaning somewhat. This states that sunspots were not visible on the poles and equator in the past, but doesn't say anything about the present!

(E) appear as dark spots on the Sun's surface, which have never been sighted on

This option does use the correct verb tense, but it is still INCORRECT because it uses the term "appear" rather than "visible," which is much clearer.

As you can see, starting your process with #2 on our list is much more complicated and doesn't help you eliminate large chunks of options easily. You can certainly answer a question this way, but it may take you MUCH longer to arrive at the correct answer!


Don't study for the GMAT. Train for it.

Dear Friends,

Here is a detailed explanation to this question-
Meaning is crucial to solving this problem:
Understanding the intended meaning is key to solving this question; the intended meaning of this sentence is that sunspots are visible as dark spots on the surface of the Sun but have never been sighted on the Sun's pole or equator.

Concepts tested here: Meaning + Tenses + Idioms + Grammatical Construction

• The last element in a list of more than two elements is joined to the others with the "comma + conjunction" construction, and the others are joined with commas.
• The present perfect tense (marked by the use of the helping verb “has/have”) is used to describe events that concluded in the past but continue to affect the present.
• The present perfect continuous tense (marked by "has/have been") is the correct tense to refer to actions that started in past and continue into the present.
• The simple past tense is used to refer to events that concluded in the past.
• The preposition "on" is used to refer to a location on a flat plane.

A: Correct. This answer choice uses the phrase "but have never been sighted on", conveying the intended meaning - that sunspots are in general visible as dark spots on the surface of the Sun, but have never been sighted on the Sun's poles or its equator. Further, Option A correctly uses the present perfect tense verb "have...been sighted" to refer to an event that concluded in the past but continues to affect the present. Additionally, Option A avoids the grammatical construction error seen in Option B, as it correctly uses conjunction ("or" in this case) to join two elements in a list "the Sun’s poles" and "equator". Option A also correctly uses the preposition "on" to refer to a location on a flat plane (the surface of the Sun). Besides, Option A is free of any awkwardness or redundancy.

B: This answer choice alters the meaning of the sentence through the phrase "never have been sighted on the surface of the Sun"; the construction of this phrase incorrectly implies that sunspots are visible as dark spots in some unspecified area and have never been sighted on the Sun's surface, poles, or its equator; the intended meaning is that sunspots are visible as dark spots on the surface of the Sun, but have never been sighted on the Sun's poles or its equator. Further, Option B incorrectly joins the first two elements in a list - "surface of the Sun" and "the Sun's poles" without a comma and joins the last element - "equator" - with conjunction ("or" in this sentence); please remember, the last element in a list of more than two elements is joined to the others with the "comma + conjunction" construction, and the others are joined with commas.

C: This answer choice incorrectly uses the simple past tense verb "sighted" to refer to an action that concluded in the past but continues to affect the present; please remember, the present perfect tense (marked by the use of the helping verb “has/have”) is used to describe events that concluded in the past but continue to affect the present, and the simple past tense is used to refer to events that concluded in the past. Further, Option C incorrectly uses "at" to refer to a location on a flat plane (the surface of the Sun); please remember, the preposition "on" is used to refer to a location on a flat plane. Additionally, Option C uses the needlessly indirect phrase "appear as", leading to awkwardness.

D: This answer choice incorrectly uses the present perfect continuous tense verb "having been sighted" to refer to an action that concluded in the past but continues to affect the present; please remember, the present perfect tense (marked by the use of the helping verb “has/have”) is used to describe events that concluded in the past but continue to affect the present, and the present perfect continuous tense (marked by "has/have been") is the correct tense to refer to actions that started in past and continue into the present. Further, Option D incorrectly uses "at" to refer to a location on a flat plane (the surface of the Sun); please remember, the preposition "on" is used to refer to a location on a flat plane. Additionally, Option D uses the needlessly indirect phrase "appear as", leading to awkwardness.

E: This answer choice subtly alters the meaning of the sentence through the phrase "which have never been sighted on"; the construction of this phrase incorrectly implies that sunspots are visible as specific dark spots on the Sun's surface that have never been sighted on its poles or equator; the intended meaning is that sunspots are in general visible as dark spots on the surface of the Sun, but such spots have never been sighted on the Sun's pole or equator. Further, Option E uses the needlessly indirect phrase "appear as", leading to awkwardness.

Hence, A is the best answer choice.

To understand the concept of "Present Perfect Tense" on GMAT you may want to watch the following video (~2 minutes):



To understand the concept of "Present Perfect Continuous Tense" on GMAT, you may want to watch the following video (~1 minute):



All the best!
Experts' Global Team

Here is the structure of the sentence:

Sunspots are visible as dark spots on the surface of the Sun but have never been sighted on the Sun’s poles or equator.

(A) are visible as dark spots on the surface of the Sun but have never been sighted on

'but' joins two verb phrases and they both work with the subject 'Sunspots':
- Sunspots are visible as dark spots on the surface of the Sun
- Sunspots have never been sighted on the Sun’s poles or equator

The situation does require contrast in the sense of 'yet' and 'but' serves that purpose. Sunspots are visible as dark spots on the surface but have never been sighted on the poles or equator. Sounds good.

(B) are visible as dark spots that never have been sighted on the surface of the Sun

Total wreck. Not sure what it even means. We know that they have been sighted on the surface.

(C) appear on the surface of the Sun as dark spots although never sighted at
(D) appear as dark spots on the surface of the Sun, although never having been sighted at

'although' means 'in spite of the fact that...' It doesn't work here as well as "but" does.

Think about it:
In spite of the fact that they have never been spotted on the Sun's poles or equator, sunspots are visible as dark spots on the surface of the sun.
So "although" takes on the meaning that something is true in spite of something else. That is not what we want to say.

'Although' would work in something like this:
Although the sun is about 150 million kms away from us, sunspots are visible as dark spots on its surface.
Now here that meaning comes through. The clause after 'although' gives us a fact which makes the main clause unexpected. Since the Sun is so far away from us, we may expect that sunspots will not be visible to us but they are.

If the sunspots are not visible at the poles or equator does it mean that we would expect that they should not be visible on the surface too? No.
The point is that they are visible on the surface but not at the poles. Just two contrasting situations.
Hence, the relation that 'although' proposes does not exist here.

Also, the dependent clause starting with 'although' is reduced usually when it appears before the main clause and talks about the same subject.

Although the Sun is very far from us, it provides enough heat and light to make life possible here.
Although very far from us, the Sun provides enough heat and light to make life possible here.

We know that 'very far from us' is talking about the Sun, which appears right after the comma.

Consider: The Sun provides enough heat and light to make life possible here although very far from us.
What is 'very far from us'? The life that Sun supports? Or the Sun?

Hence, (C) and (D) should be eliminated.

(E) appear as dark spots on the Sun's surface, which have never been sighted on

With the use of 'which,' two problems have come in:
- 'which' refers to 'dark spots,' not surface, the preceding noun. We may still accept it.
- the contrast is lost.

Hence, this is not the best option.

Answer (A)

I choose A as my answer.
What you need to know is that "visible" is an adjective. You should also know that past participle is also treated as an adjective. Here's an example of a past participle, which is always used as an adjective:

1) The man carried a broken window. ---> the "broken" is a past participle describing the "window", which is a noun.

As for the question regarding "sighted', it means that its a verb that doesn't need to be followed by an object. For example:

2) Tom runs ---> you don't have to say where did Tom run. The verb "runs" can stand by itself without the need to add an object. However, some of the verbs will NEED to be followed by an object to complete the thought of the sentence. For example:

3) Tom completes his homework ----> can you imagine how odd it will be if the sentence were written without "his homework"? So this shows an example of some verbs that MUST be followed by an object.

I will have to disagree with you because I feel that "sighted at" suggests the location of the sighting. For example:

A huge fight was sighted at the construction site ----> it means that those who saw the fight were also there at the construction site.

So when you look at option C, it suggests that someone wasn't able to see the sunspots when he or she was at the sun's poles or equator. Unless that person is Chris Angels, I don't think that such a stunt can be possible....lol

I have chosen A for this question:

A. The two verbs are parallel here. "Are visible" tells us that this fact is true in the current time and is parallel to "have never been sighted" that suggests we have still not been able to see these sunspots on the poles or equator of the sun. Although the tenses are different, it is still parallel because of the meaning of the sentence. The use of "are" gives us correct subject verb agreement.

B. The last part of this answer choice makes no sense. "Sighed on the surface of the sun then sun's..." is definitely not correct.

C. I had 2 issues with this answer choice. Firstly, the simple past tense of the verb "sighted" suggests that this fact occurred in the past and is not valid in the current time frame, so we are left wondering if this is true or not in the present time. I believe the intention of the sentence is that we have not been able to see these sunspots on the poles or equators in the past and that fact continues today. Therefore, simple past tense usage is incorrect. Also, I was confused by the use of the word "although" because it starts off a subordinate clause, but this clause does not have a subject.

D. The subordinate clause set off by the word although does not have a subject.

E. Which seems to modify sun's surface.

Sunspots, vortices of gas associated with strong electromagnetic activity, are visible as dark spots on the surface of the Sun but have never been sighted on the Sun's poles or equator.

(A) are visible as dark spots on the surface of the Sun but have never been sighted on
(E) appear as dark spots on the Sun's surface, which have never been sighted on

Let us first start with the modifier doubt regarding “which”. Generally, “which” refers to the immediate preceding noun. However, that is not the case always. It can also refer to a little far away noun as well. Following is the link to the article that explains in detail when “which” can refer to a slightly far away noun:

https://gmatclub.com/forum/noun-modifier ... 35868.html

In choice E, “which” can only refer to the immediate preceding noun “Sun’s surface” because “on the Sun’s surface” modifies the verb “appear”. Where do the dark spots appear? On Sun’s surface.

Hence, “Sun’s surface” can also be placed right after “appear”. That is the reason why “which” cannot jump over “Sun’s surface” to refer to “dark spots”.

I will suggest that you go through the article first and then read my explanation again. Then it will be absolutely clear to you, why “which” in option E only refers to “Sun’s surface”. This incorrect modification leads to incorrect meaning, making choice E incorrect.

Hope this helps.
Thanks.
Shraddha

Hii Shraddha.
I had been through the SC course in which I was told that unless there is some quantity word, the subject cannot reside inside a prepositional phrase.
So as per that, I feel why shouldn't the "which" modifies the dark spots and not "Sun's surface".
Consider the example:
Most of the Indians, who are generally good at quant, prefer taking CAT.
IMO, I am talking about Indians in general and not about 80% of the Indians.

Now consider this"
The box of nails, which is black in color, is kept upon the table.
IMO, here which refers to "the box" and not "nails".

Please clarify.
Regards.

Hi Marcab,

Let’s begin from the basic, relative pronoun modifiers, or for that matter any noun modifier, modifies the immediate preceding noun entity. This noun entity can be a single word or a noun phrase. If the modified entity is a noun phrase, then the number of the head of the noun entity decides the number of the verb. Let’s take a set of examples here:
1. The box of nails that are rusted is kept on the table.
2. The box of nails, which is black in color, is kept on the table.

In sentence 1, relative pronoun “that” refers to “nails”. The verb after “that” is plural that makes it clear that the DC is talking about the “nails”.

In sentence 2, “which” refers to “the box”. Here again the verb “is” tells us what “which” stands for.

Now, this is a very common confusion that a subject cannot lie in the prepositional phrase. Here I would like to elaborate a bit. This rule that subject cannot be in the prepositional phrase only applies to the SV number agreement.
In both above mentioned examples, the verb of the IC is “is” because the subject of the sentence is “the box”. In such constructions, “nails” or the noun entity that lies in the prepositional phrase cannot be the subject. Hence the number of the subject decides the number of the verb.

However, this rule does not apply to the modification of the relative pronouns. Relative pronouns can refer to any noun in the noun phrase preceding it, even if that noun lies in the prepositional phrase as is evident form the above mentioned examples.

Now intheofficial question of Sun SPots, I have already explained in my earlier post, why "which" cannot refer to "dark spots". You can understand the reasoning by reading the article "Noun Modifiers can refer to far away nouns" the link to which has been provided in that post.

Hope this helps.
Thanks.
Shraddha

Pretty interesting query. The doubt in this question really is - can active voice be parallel to passive voice?
I will explain this using a different question and then will look forward to you applying this logic to the question in this thread.

Another Official Sentence

Dressed as a man and using the name Robert Shurtleff, Deborah Sampson, the first woman to draw a soldier’s pension, joined the Continental Army in 1782 at the age of 22, was injured three times, and was discharged in 1783 because she had become too ill to serve.

Doubt raised
Although the above sentence is correct, 'joined' , ' was injured' , and 'was discharged' do not seem parallel to me.

Doubt Clarification

Active voice can be parallel to passive voice.

In this sentence we have three actions related to Deborah:
1) Deborah joined
2) Deborah was injured
3) Deborah was discharged

Thus here, active verbs are parallel to passive verbs. Logically, the above is the only way we can express these. If we were to make everything in active voice, then we will lose the preciseness and effectiveness of the sentence: “Deborah joined the army; enemies injured her; army discharged her...”. This is highly complex and not effective at all.

Thus, active verbs can very well be parallel to passive verbs when the context requires!

Now say we have a sentence:
Mouse ran up the clock, and water spout was climbed by the spider.

This sentence is not parallel since the two clauses do not have logically parallel subjects because of use of different voice. It should be made parallel as follows:
Mouse ran up the clock, and spider climbed the water spout.

Here is one more sentence:
Mary cooked elaborate dinner, which was indulged by all the guests.
This sentence is correct as is: First part is active voice and second part - which clause is in passive construction.

Thus, it really depends on the context of the sentence if active voice can be made parallel to passive voice. The end goal is to communicate the idea in the most effective manner.

I hope this helps. Now apply the same logic to the Sunspots question.

Thanks,
Payal

The correct parallel structure in the original sentence emphasizes the contrast between where sunspots are found {are visible... Sun) and where they are not {have never been sighted... equator). Sunspots is the subject of the sentence; are is the verb of the first part of the contrast, and have been sighted is the verb of the second. (The adjective visible is a complement and is parallel to the past participle sighted) Both parts of the sentence conclude with phrases indicating location.The contrast itself is indicated by the conjunction but.

A Correct. This sentence clearly and correctly draws a contrast between where sunspots are found and where they are not.
B The modifying clause that never... Sun distorts the meaning of the sentence; also,without punctuation, the phrase on the surface of the Sun the Suns poles or equator is ungrammatical and makes no sense.
C Although typically introduces a subordinate clause, which has a subject and a verb,but here there is no subject and "sighted' is not a complete verb.
D Although usually introduces a subordinate clause,but there is no subject of the clause and having been sighted is not a complete verb phrase.
E This phrasing makes the sentence somewhat awkward and unclear.

Hi e-gmat,

Please can you answer my queries below regarding the above OG question.

1. When compared to sighted at equator, sighted on equator sounds good and I feel we must say sighted on equator and not sighted at equator as equator is not a place like an area in a city. Please can you let me now if my understanding above is correct and can I eliminate an option based solely on this one?

2. Consider the sentence, Sunspots appear on the surface of the sun as dark spots although never sighted at equator. Can I assume sighted is a verb - ed modifier which modifies the previous noun Dark Spots? or the presence of although would restrict sighted as a verb-ed modifier?

3. Consider the below two sentences:
a. Sunspots are visible as dark spots on the surface of the sun but have never been sighted on equator. (X but Y)
b. Sunspots appear on the surface of the sun as dark spots although never sighted at equator. (X although Y).

In sentence (a) can I say the parallelism rules allow the sunspots to be the subject in both X and Y clauses? If the answer is yes for the above question I assume then the same holds true for (b) also. Is my understanding correct?

While attempting this question I felt the construction X but Y is not appropriate (for I think X, but Y is the correct form) and hence eliminated option A and selected C thinking that the "sighted" is acting as verb-ed modifier for dark spots. However, I was wrong. Please could you elaborate your answer for my 3 queries above?

Hi there,

1. I would say this is a question of usage rather than of application of logic. The sentence says that sunspots have been sighted on the surface of the sun but not on the poles or equator. So, I would pick 'sighted on' based on the context of the sentence rather than the meaning that you've applied.

For questions 2 and 3, the only correct use of 'although' that I've seen in such a context in official questions is when the meaning is completely unambiguous. For example, in the sentence "Although small, the conference room suits our needs," it is clear that "small" can refer only to the conference room. In a context in which it's possible for the modifier to refer to more than one item, it makes more sense to replace the modifier with a verb that is parallel to the verb in the previous clause, so that the meaning is absolutely clear.

I hope this helps.

Regards,
Meghna

Responding to a PM:

1. Can you throw some light on sighted on vs sighted at usage in terms of meaning.
"Sighted on" can be used to refer to a surface, a line or a point. "Sighted at" can be used to refer to a location. Since poles / equator can be considered points/line or location, both the usages would be alright.
2. Why although usage is incorrect here in options.
As per the OE, "although" should be used to introduce a clause.
3. Sighted or have been sighted is mentioned as not a complete verb? Why? What does it need more?
"Sighted" is not a complete verb - since the usage is in passive voice, complete forms would be "is sighted", "was sighted" etc.
" Have been sighted" is definitely a complete verb. (passive -present perfect)
4. Is there no difference in between Sunspots visible as dark spots and Sunspots appear as dark spots?
In some cases the meaning can be different:
"Appear" may mean " to become visible" (i.e., something was not visible before, but now it is):
Madonna appeared on the stage.
"Visible" does not imply so:
She was visible because of her bright dress.

I read one of the articles from magoosh in which it said that Although needs a clause(subject and a verb) but there are many instances in OG where such conjunctions have not been followed by a clause.
Eg-
Q48 from OG13: Though called a sea, the landlocked Caspian is actually the largest lake on Earth, covering more than four times the surface area of its closest rival in size, North America's Lake Superior.
(choice c and it is the correct answer).

OG13 - Q36: Along with the drop in producer prices announced yesterday, the strong retail sales figures released today seem like it is indicative that the economy, although growing slowly, is not nearing a recession.
(although portion is not underlined)

But in one explanation it says that it is needed.
OG 13 Q 17:
Sunspots, vortices of gas associated with strong electromagnetic activity, are visible as dark soots on the surface of the Sun but have never been sighted on the Sun's poles or equator.
(A) are visible as dark spots on the surface of the Sun but have never been sighted on
(B) are visible as dark spots that never have been sighted on the surface of the Sun
(C) appear on the surface of the Sun as dark spots although never sighted at
(D) appear as dark spots on the surface of the Sun, although never having been sighted at
(E) appear as dark spots on the Sun's surface, which have never been sighted on

here the official guide explanation for although(option c &d) says:

C. Although typically introduces a subordinate clause, which has a subject and a verb,but here there is no subject and sighted is not a complete verb.
D. Although usually introduces a subordinate clause,but there is no subject of the clause and having been sighted is not a complete verb phrase.

What is the correct way ? Please explain.

Dear pramitmishra0607,

I'm happy to respond. First of all, let me commend you, my friend, for asking an excellent question! It's clear that you put tremendous thought and effort into the question you are asking, and that's wonderful. Asking excellent questions is one of the habits of excellence!

The answer to this is subtle. The word "although" is a subordinate conjunction, and as such, it introduces a full clause, a dependent clause. It must be followed by a full clause. The catch, though, is that small words, e.g. [pronoun] + ["to be" verb], in the clause can be dropped if they are implied, so what is printed on the page will not look like a full clause, but it really is a full clause.

For example, from SC13 above:
Though it is called a sea, the landlocked Caspian is actually . . .
The words "it is" are implied, and with those, what follows "though" is a full clause.

From SC36 above:
. . . it is indicative that the economy, although it is growing slowly, is not nearing a recession.
Again, the word "it is" are implied, making what follows "although" a full clause.

In SC17 above, there's no way to put in a pronoun plus an auxiliary verb to turn what's following the "although" in (C) & (D) into full clauses.
(C) appear on the surface of the Sun as dark spots although they never are sighted at the Sun's poles or equator.
That doesn't work. The word "sighted," by its very nature, is a participle that is not part of an ordinary full verb. (D) is even worse: I have no clue what anyone would put in front of "having been sighted"---we can't really change perfect participles into full verbs.

That's the difference between, on the one hand, SC13 & SC36, and on the other hand, SC17. In the former two, we can insert an implied [pronoun] + [auxiliary verb] to turn what's there into a full verb. In the latter, we do not have that option, so the construction is wrong.

Does all this make sense?
Mike