What’s the correct answer !

A. They have been enemies and Greg isn't used to being friendly or having anything in common with her.

Explanation:

Without knowing anything about the context, and through process of elimination, this is the only answer that makes sense.

B and C Don't seem to work because it isnt stated that Greg is worried or embarrassed.

D. Doesn't seem to work, at least on its own, because Mr. Z thinking they should be friends, with no other factors, doesn't seem like it would be overwhelming. Unless they had been enemies, had never been friendly and thought they had nothing in common. Which leads back to answer A.

you need to explain that more, your grammer just needs to be close to perfect.