B. Good. Put each word into the sentence to see if it fits.
I believe it would be B, because there are two subjects that the speaker is referring to at the beginning of the sentence; the caterpillar and the leaf. When they use the word "it" in the second half of the sentence it is unclear whether they mean to say if "it" is the leaf or the caterpillar which they are carrying to their brother.
Before ______, then _____happened
Fortunato is addicted to wine and is drunk when he meets montresor. Montresor is insulted by the things Fortunato dose and wants revenge. Fortunato thinks about Amontillado and how he can help Fortunato take a step up a level. He thinks that the whole story right up until Montresor gets him more drunk and kills him. Hope it helps ❤️