根据对话内容，从对话后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。

A: Hello, Simon. Have you seen Billy this afternoon?

B: No, Maria. Why?

A: Oh, dear. I can't find him anywhere. I don't know what to do. He should have been back an hour ago.

    1______

B: Don't worry, Maria. He could have, but he probably didn't. Did anything happen this morning? 2______

A: His birthday party.

B: Is it possible that you said something to upset him?

A: I must have. I told him we hadn't received Mr. White's reply to our invitation.

B: 3______

A: No, he left home right after that. 4______

B: Maria, I'm sure there is nothing to worry about. He is probably on his way to see Mr. Smith, or else he is 

    with Mr. White.

A: Oh, wait! There he is! And Mr. Smith is with him. 5______ He must have been to Mr. Smith's.

A. I suppose I should have called you earlier.

B. Anything else?

C. I wonder if he could have had an accident.

D. I'm afraid he might have an accident.

E. Where could he have been?

F. You are right, Simon.

G. What were you talking about before he left?