a solemn face的用法和样例：
- Indeed he has a solemn face, but he is very humorous at heart.
- How can you put on a solemn face?
- This is a solemn face five-ring flag reflects the limitations of human self-transcendence and the pursuit of a better future.
- He looked at her with a solemn expression.
- put on solemn looks; assume a solemn face