Skywalker18 wrote:
In OA- D, isn't the comma that precedes 'and' incorrect? (,and should separate two independent clauses)
I was about to reject option D but then the parallelism in option E is bad- A newly developed jumbo rocket will be able to cost less(the second part) and the comparison also has issues( than the space shuttle ; usage of can makes it better in option D ) and thus I chose option D.
(I understand that GMAT does not test punctuations )
Here's (D).
(D) A newly developed jumbo rocket, which is expected to carry the United States into its next phase of space exploration, will be able to deliver a heavier load of instruments into orbit than the space shuttle can, and at a lower cost.
Comma use is somewhat optional, and it tends to be the case that writers can at their discretion add commas to indicate pauses and emphasize portions of sentences. So, if the use of "and" without a comma is correct, adding a comma before "and' to indicate a pause probably won't make a sentence incorrect. For instance, both of the following are correct.
My dog likes running around and does so all day long.
My dog likes running around, and does so all day long.
The comma in the second version serves to separate the two thoughts a bit. If the writer of the sentence wants to separate the thoughts a bit, the writer can use a comma after "around." If the writer wants the sentence to read more continuously, the writer can write the sentence without a comma.
So, the comma before "and" in (D) simply indicates a pause. So, the presence of that comma is not a flaw in (D).
That said, (D) is not particulary well written. The structure of the wording that expresses the comparison involving the "heavier load" is quite awkward, and the parallel structure "will be able to deliver a heavier load ... and at a lower cost" is not fully logical.
So, to correctly answer this Sentence Correction question, we have to choose a choice that's clearly better than the others but certainly not perfect.