a polite expression的用法和样例：
- "Shut up" is not a polite expression.
- Sometimes, we can slo use this idiom as a polite expression, indicating that the people to whom we are speaking are much more talented than ourselves.
- It is an everyday greeting and is usually used between acquaintances. A polite expression such as “我很好”can be used as a reply.
- `Shut up' (meaning `Stop talking') is not a polite expression.
- He moved aside for her with a polite bow.