A sea urchin can crawl slowly on its tube feet sometimes propelling

OFFICIAL EXPLANATION


THE PROMPT
A sea urchin can crawl slowly on its tube feet, sometimes propelling itself with its spine, and feeds primarily on algae, occasionally eating slow moving animals such as periwinkles or mussels.

• Highlights

→ This sentence contains a compound predicate.
One subject (a sea urchin) is attached to two verbs (can crawl and feeds).
Sometimes people describe a compound predicate as "two verbs that share one subject."

→ Typically, we do not place a comma before the second verb in a compound predicate.
We want to keep subjects connected to their verbs.
Sometimes we cannot avoid placing a comma between a subject and its second verb.
This sentence is one of those instances, because a nonessential modifier that must be flanked by commas intervenes.

That is, the commas really belong to the modifier that follows the first verb phrase, this way:
. . . , sometimes propelling itself with its spine, . . .

If we remove that modifier, our core sentence is this one:
A sea urchin can crawl slowly on its tube feet ... and feeds primarily on algae.

• modifiers and modifying phrases
→ sometimes propelling itself with its spine
This modifier refers to the previous clause and in particular to the way that a sea urchin moves.

→ occasionally eating slow moving animals such as periwinkles or mussels
This modifier also refers to the previous clause and in particular, to what the sea urchin eats.

You do not see the subject in the second clause, but as I showed in the core sentence, above, that subject is implied because the sentence contains a compound predicate.


THE OPTIONS
• I do not see any errors

• too many ands
→ A sea urchin can crawl . . . and feeds . . . and will on occasion eat . . .
→ Now it appears that our compound predicate contains three verbs.
The modifier "occasionally eating slow moving animals" is turned into its own verb in this instance.

In other words, the verbs form a list: X, and Y, and Z
Just one problem. The proper form is X, Y, and Z.

• diction error: to introduce examples, such as is preferred to like
For a more in-depth explanation of the current official stance, see my other post from today, here, beneath option E in that question.

• compare to option A.
Option A is better than option B. Why? Option A uses such as to introduce examples.
Although like may soon be an acceptable word to introduce examples, the word like will not be superior to such as.
Option A is not plagued by the such as/like issue and is just as effective as option B.
ELIMINATE B

• This sentence is a run on, and in this special case, a comma splice
→ We cannot "stick" two independent clauses together with nothing more than a comma.

→ To join independent clauses, we may use:
1) COMMA + CONJUNCTION (and, but, so)
2) SEMICOLON, no conjunction
3) SEMICOLON, conjunctive adverb

Please familiarize yourselves with these three rules.
I would recommend reading this short article, here.

→ Look at our core sentence:
A sea urchin can crawl slowly on its tube feet and feeds primarily on algae.

This sentence (option C, the comma splice) changes the core sentence incorrectly, this way:
A sea urchin can crawl slow on its tube feet, it feeds primarily on algae.
→ that comma needs to be followed by a coordinating conjunction (FANBOYS)

• it does is a bit dicey.
When one subject does two things, we typically do not repeat the subject before the second verb or insert a pronoun to stand in for the subject.
This guideline is fairly strict; GMAC writers value concision.
ELIMINATE C
• illogical
→ so that suggests purpose or result, neither of which makes sense here.
→ The sea urchin feeds primarily on algae, but not so that it can occasionally eat other slow moving animals.

• diction: use such as rather than like to introduce examples
ELIMINATE D

• the plural pronoun they does not agree with the singular subject the sea urchin.
ELIMINATE E

The best answer is A.

COMMENTS

Shikhar22 , aarkay87 , and Kinjal786 , welcome to SC Butler.

All aspirants have a standing invitation to post.

Gknight5603 , you ask a good question.
You asked:
Kinjal786 mentions the answer.

Eating slow moving animals such as periwinkles or mussels modifies the previous clause because that clause talks about what the sea urchin eats.
This sentence contains a compound predicate.
So the clause before the "eating" modifier is this one:
[The sea urchin] feeds primarily on algae, → occasionally eating slow moving animals

I describe the compound predicate in this sentence—the second part contains an implied subject, so the modifier can indeed modify that clause.
See above, in the notes just below the prompt.

These answers range from good to excellent.
Better yet, they are easy to understand.

Nice work!