The second choice is a fragment, not a complete sentence.
I believe the correct choice is number one, because if you turn the sentence around, it answers the question of why the crowd is gathered. You may want to confirm on the website chompchomp.com (Grammar Bites).
The first answer is incaple of during his math homework
The answer is c, because it is clearly not an alliteration, and there is no repetition. An end rhyme is when words on the end of lines sentences rhyme with the words on the ends of other sentences; where as an internal rhyme has rhymes in the same sentence.
