Thank you so much for your help :)

Your answer is better than the key, in my opinion. They both miss a little subtlety in the original, though. In the original, "man" is used without an article, to represent all men, or mankind. The verb choice, "is", is in the indicative: it indicates that man is wise. In spite of this ("Although"), he may make mistakes. This last part of the rewrite is not in dispute: all three versions you show use it. So let's look at the first part. In your version, your choice of a subjunctive "may be", however elegant, shifts the meaning a little, as you can see. The original leaves no doubt - man is wise. The key version, though, is worse: its choice of using an article breaks the use of "man" as a symbol of mankind and turns it into a comment on a particular man. I hope this is helpful.

I think your answer is correct and the answer key is wrong. The original sentence didn't have "the" before "man", so there's no reason to add it in the answer. It is talking about humans in general, not any particular man.

Both the sentences are grammatically correct. However, the meanings are different. Your sentence is about mankind/humans since you have not used an article. The other sentence is about a specific man as Shannon said.

You are missing the article. By adding the after wise indicates you are talking about a specific man.