swim in a river的用法和样例：
- Do you usually swim in a river or a lake?
- Have you ever swum in a river or a lake?
- Swimming in a river in summer is a lot of fun.
- Jeff: Have you ever swum in a river or a lake?
- It's so hot. What I want to do now is to have a swim in a river.
- I went fishing and swam in a river.