Official Guide B/B #9 (spoiler)

I was thinking of choosing D at first but I couldn't really reason my way through this one. Can somebody explain why A or B would be incorrect? I assumed that chloramphenicol didn't inhibit translation at a specific concentration or that the incubation time was too short. I'm not sure why these would be wrong and AAMC didn't really go in depth with their...

Official Guide B/B #9 (spoiler)