The film was directed by a man ______ is not well-known.

• A. What
• B. Who
• C. That
• D. Whom

Answer: (B)

This tests choosing the correct relative pronoun for a person in a defining relative clause. The man is the subject of the clause “is not well-known,” so the pronoun must be the subject form for people. That form is who, giving: a man who is not well-known. Whom would be used if the pronoun were the object of the clause, as in a man whom the director met. What isn’t used for people, and that is less formal for people in this context, though sometimes seen in everyday speech. So who fits best here because it correctly stands as the subject of the relative clause.