The sentence that contains an antecedent that is unclear, missing, or confusing, is B) During the announcements this morning, they said that football practice was cancelled.
Who does <em>they </em>refer to? There is no antecedent.
What poem? You didn't say.
The first one. The commas are correctly placed. Sorry if this is wrong.
"Why did Leonard decided not to go to the lecture?" is a a question because it is asking why, therefore it should have the question mark.
