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?