a three-pin plug的用法和样例：
- Operation rules should be strictly followed. The instrument adapts with a mono phase three pin plug, which connects to the earth for safety.
- three pin plug
- It is a three ring circus to watch that silly dog play.
- This three pin is still fixed on her left knee.
- He discarded a three,and picked up a Queen.
- There are still three pins left.I bowled a spare.