Definite article is used before a noun (person place or thing) to indicate that the identity of the noun is known to the reader.
indefinite article is used before a noun that is general or when its identity is not known.
I would assume the answer to your question is A. “Because only men have the Y chromosome, so the women i. the class wouldn’t be able to participate.”
it just as it is tempting to take natural selection to extreme so no not all
