Can someone explain how the answer is right and C is not right?

Actually I meant "how B is not right?" I chose B

Hey B is wrong because it doesn't matter if one planet can block it because the passage say it unlikely, "any large planets form" so it is irrelevant if one planet will suffice because they normally wont have even one

I also chose B, but afterwards realized that B talks about intelligent life "surviving" a comet, whereas the paragraph states that it is unlikely for life to "emerge" on a planet. This points that the real issue with comets is not that they would kill intelligent life, but that they would prevent it from emerging in general.

Just wanted to note that both Dylan and Kellen brought up valid reasons to dismiss d.