Please explain why B isn't correct?

I understand why D also works, but for rule substitution questions- arent we just looking for a condition that would have the same chain reaction? With B, we still get the H->GK chain and it specifies that H cannot be first because either F or M have to be. I also understand why D works and has the same chain reaction. This questions is super tricky! Can a tutor please provide an explanation on this?