So I normally use the word Climax but I'm assuming that climax and main action are the same thing. The main action is definitely (B) - Mary's husband tells her that he is leaving her, because that is what starts the suspense.
Please tell me if that isn't right, I think it is.
I believe the closest antonym would be worsen
hope this helps
Answer:
The killer had left a trail of blood on the floor
C is the correct answer mate