Duìbuqî. I’m sorry.

Example 1:
A: Duìbuqî, wô bâ nî de shü nòngdiü le.
B: Méiguänxi, wô zài mâi yì bên.

A: I’m sorry, I lost your book.
B: It doesn’t matter. I’ll buy a new copy.

Example 2:
A: Wô yòu chídào le, duìbuqî.
B: Kuài qù göngzuò ba, xià cì zhùyì.

A: I’m late again. Sorry.
B: Get to work and don’t be late again.

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If you ever think you’ve done something improper, you may use this commonly used expression to ask for forgiveness.

Synonymous Expressions
Qîng yuánliàng!
(e.g. Qîng yuánliàng, dârâo nín le. - Excuse me for interrupting you.)