The correct answer is D. No article.
The word "man" in this sentence is not a specific man, but rather a general term for all humans. Therefore, we do not need to use an article.
If we were to use an article, it would imply that we are talking about a specific man. For example, if we said "Man is a social animal," we could be talking about a man who is particularly outgoing and enjoys spending time with others. However, if we say "Man is a social animal," we are simply stating that humans are social creatures.
It is important to note that there are some cases where we can use an article with the word "man." For example, if we are talking about a specific man's job, we could say "He is a man of the law." In this case, we are using the article "a" to indicate that we are talking about a specific man.
However, in the sentence "Man is a social animal," we are not talking about a specific man. We are simply stating that humans are social creatures. Therefore, we do not need to use an article.
