If you have not caught what the guest said, you may say:
A. What did you say, sir?
B. Uh?
C. What do you mean?
D. I beg your pardon?
When you express your apologies to your guest you may say "I beg you pardon, sir" in rising tone.
A. 对
B. 错
When you ask the guest to repeat what he says you may say "I beg you pardon, sir" in rising tone.
A. 对
B. 错
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