( My grandson thinks he can cook better than any other person at the fair; and he) has the blue ribbons to prove it.

A) My grandson thinks he can cook better than any other person at the fair; and he

B) My grandson thinks he can cook better than any other person at the fair, and he

I put choice A but the answer was choice B. Could you also please explain when it is is appropriate to put a semi colon versus a comma?

I’ve got what I think is a pretty good tag-team explanation of that in this post.