I came across this question today in GMAT prep and choose D.
Instructors any thoughts why C is correct as "comma + but" should follow an independent clause.
Although I understand but and yet seem to be redundant, I cannot reason out C.
1 -- MOST IMPORTANTPUNCTUATION IS NOT TESTED! DO NOT WORRY ABOUT PUNCTUATION!
in choice (c) the commas are a non-issue anyway; they belong to the modifier, not to the overall structure of the sentence. (try removing the modifier; you should be able to write the remaining sentence without that comma.)
among the main reasons why punctuation isn't tested is that it is inconsistent. in particular, longer
sentences tend to use more
punctuation, and shorter sentences tend to use less.
for instance,i tried hard but failedi tried hard, but failed
both acceptable; the difference is mostly rhetorical (and 100 percent outside the domain of the gmat).i tried as hard as i could until i was totally exhausted, but failed anyway
--> this one pretty much has to be written with the comma, because without the comma it's essentially unreadable. (take out the comma and see how weird it becomes.)
most importantly, though, refer to #1 above.