a pair of compasses的用法和样例：
- The teacher asked us to buy a pair of compasses.
- It is easy to describe a circle if you have a pair of compasses .
- It is easy to describe a circle if you have a pair of compasses.
- I bought a pair of tan leather shoes the other day.
- Billy has a pair of new trousers.
- This small animal has a pair of hazel eyes.