A Mars rover is an automated motor vehicle that propels itself across

OFFICIAL EXPLANATION


THE PROMPT

THE OPTIONS

• modifier error
→ A participle modifier (a verbING word) such as helping without a comma modifies the immediately preceding noun, so helping modifies Mars or, more likely, conditions.

→ Neither the conditions nor the planet Mars helps scientists determine whether life ever existed on Mars.
Nonsensical.

→ Suppose that we allow "helping" to modify "territory and conditions" [on Mars]?
The meaning is still ridiculous.
Territory and conditions cannot help scientists determine something.
Now, the observations about the territory and conditions could help (and do help, according to the correct answer), but helping cannot reach that far back to modify observations.
We would need a comma after Mars and before helping, in which case the word helping would refer to the previous clause, including observations.
We do not have such a comma.
Eliminate A

• modifier error
→ with usually means alongside; this modifier does not make much sense.

→ If we parse the sentence, the meaning is silly:

The Mars rover vehicle propels itself across the surface of Mars,
gathering observations, [and]
with information helping scientists?
The vehicle is traveling with information helping scientists? No.
Nonsensical.

At the least, the modifier is "tacked on." It is not clear what with information helping is supposed to modify.
Eliminate B

• modifier error
→ First, let's talk about what is correct: that help refers to conditions.
That must refer to conditions because the verb help is plural, as is the noun conditions. The word Mars is singular.
Essential modifiers (such as prepositional phrases) and short phrases are allowed to come between the word that and its noun.
See Notes, below.

→ The error? As is the case in option A, the conditions cannot and do not help the scientists.
Two nearly identical answers cannot both be correct.
This option's modifier error is enough, by itself, to eliminate (C).
The fact that options A and C are similar just reinforces what we already know. Neither is the answer.

• modifier is correct
• the phrase in blue typeface is a special kind of modifier (and a special kind of appositive).
It is called a summative modifier. (Think, "summary.")
When we need to emphasize an idea expressed in the previous clause, or "summarize" that idea with a noun, we use a summative modifier.
They are very common in formal writing.

→ the word information "summarizes" the fact that the rover is gathering observations about the territory and conditions on Mars.
This information will help scientists to determine whether life existed on Mars.

This sentence is leagues better than any of the others.
I do not want you to hunt for the best sentence.
Find the four worst sentences and eliminate them.
That said, part of deciding which options are the four worst often entails comparing options to one another.

In this case, option D clears up all the modifier confusion or murkiness and sets forth a crisp sentence that is easy to follow.
KEEP

• pronoun antecedent is unclear
→ does those refer to conditions? to observations?
Those probably refers to observations, but with the verb tense error in this sentence, I would not make things worse by using a potentially vague pronoun.

• improper verb tense
→ the past tense helped does not fit.
If the rover has already helped scientists to determine whether life existed on Mars, then the first part of the sentence should be in past tense, too.
That is, if the rover helped the scientists, then the rover IS not now propelling itself across the surface (in order to help the scientists).
ELIMINATE E

The correct answer is D.

NOTES

• future tense?
We might notice the lack of future tense in every option except (D).
This issue is not dispositive.
Although future tense makes more sense (the information WILL help scientists to determine something), we could reasonably assert that the Mars rover is currently propelling itself across Mars; that the rover is now gathering observations; and that whatever is doing the helping, the scientists are now in the process of determining whether life existed on Mars.
In other words, the lack of future tense in any option may make it inferior to option D by comparison, but on its own is not enough to eliminate an answer.

[Sidebar: An ___ING word does not have a tense and follows the tense of the verbs in the main clause.
In options A and B, we are dealing with is and propels, so helping scientists to determine whether life ever existed on Mars happens in the present. The scenario is not implausible.

• THAT - can modify a slightly faraway noun.

Both that and which and other kinds of noun modifiers can modify the head noun in a noun phrase such as conditions on Mars.

(1) The underground corridor system at Harvard Law School that was built to protect students from bitter winter cold routinely confounded my sense of direction; during my first year, I finally just stayed close to section mates who knew where our next class was located.

That refers to an underground corridor system. This much I promise: Harvard Law School was not built to protect students from bitter winter cold.

The problem is that two essential modifiers cannot both be in the same place.
By convention, we just put one first.

At which law school are the underground corridors?
Not at Stanford or at Yale.
In other words, those corridors are at Harvard Law School. (And yes, I got lost constantly.)

Why were and are students running around beneath the buildings of a law school in corridors?
What is distinctive about this system of corridors?
Answer: The system of corridors is distinctive because it was built to protect students from brutally cold New England winters.
A student can get to most classes on frigid days in warm hallways.
In my example sentence, that inthat was built refers to to a slightly distant noun.

For a good (and unofficial) question in which I discuss how that can be somewhat far away from its noun, see this post, here.

COMMENTS

Boho and hiteshdusseja , welcome to SC Butler.

I am glad to see you both.

All aspirants have a standing invitation to post.
You can post an explanation, ask a question, or point out something interesting.

Shikhar22 , your analysis is spot on.

zhanbo , I am bumping you to Best Community Reply.

All of these answers, questions, and replies to questions are good.

Kudos to all.
Very nicely done.