Elimination is always the best. Pick out the worst possible answers, so it'll give you less choices to pick from. Or you could always pick c. I wouldn't advise that. Good luck on your test. :)
Answer:
topic sentences state the main idea.
Answer:
The answer is b. Micro-meteor-oids
Explanation:
The best correction of the clause fragment is to C. delete the word "although."
Without that word, you get a proper single independent sentence, and not a fragment.