21. Tina: Hello! May I talk to the marketing director, Mr. Walter?
Cynthia: Sorry, he is not in right now. _____________
Tina: That’s all right. Do you know when he’ll be back?
Cynthia: He should be back by four.
(A) May I have his cell phone number?
(B) Shall I take a message?
(C) I’d like to leave a message.
(D) May I call back later?