The correct answer is D. no article.
A one-act play is a play that is performed in one act, which is a continuous section of a play. One-act plays are typically shorter than full-length plays, and they often focus on a single event or situation.
The article "a" is used before singular nouns that refer to a general or indefinite thing. For example, "I saw a dog." The article "an" is used before singular nouns that begin with a vowel sound. For example, "I saw an apple." The article "the" is used before singular nouns that refer to a specific or definite thing. For example, "I saw the dog that bit me."
In the sentence "It is . . . . . . . . one act play," the noun "play" is singular and does not refer to a specific or definite play. Therefore, the article "a," "an," or "the" is not necessary.
