The correct answer is D. no article.
A one-man show is a theatrical production that is performed by a single actor. The actor may play multiple roles, or they may play a single role that is the focus of the show. One-man shows can be based on true stories, fictional stories, or a combination of both. They can be comedic, dramatic, or both.
The use of an article in front of the noun “show” depends on the context. If the show is a specific show that is being referred to, then the article “the” would be used. For example, “I saw the one-man show that was playing at the theater last night.” However, if the show is a general type of show, then no article would be used. For example, “I like going to see one-man shows.”
In the case of the sentence “It is . . . . . . . one man show,” the show is not being referred to specifically. It is simply being described as a one-man show. Therefore, the correct answer is no article.