Hi Shahd,
Hmm...I see what you are saying. These after-class practice sets are great for extra practice if you really want to nail a concept, but sometimes the wording can be a bit difficult. I would say that both of these answers would be good contenders for the correct answer, as both argue the same concept. In an actual MCAT exam, you have the opportunity to argue that one question is ambiguous in that two of its answers could be considered correct.
Hope that helps, happy studying!
Cheers,
Molly