Guest: Oh, I hadnt realized how late it was. Im afraid Ill have to be going. Host: Oh, not yet. I

Guest: Oh, I hadn't realized how late it was. I'm afraid I'll have to be going. Host: Oh, not yet. I'm just going to make some coffee. Guest: ______ , though I'd really love to stay. I've got to be up by six tomorrow morning, unfortunately. Thank you for a wonderful party.

A．I'm sorry, but I must

B．Excuse me, but I have to go

C．Pardon me, but I should go

D．It's a pity, but no way out

A解析：主人诚心挽留，客人坚持要走。由于不能接受主人的好意，客人应表示歉意，故而选择A．I'm sorry，but I must比较合理。其他选项使用场合不当。