bring coals to newcastle

• vi. 多此一举(做徒劳无益的事；白费力气；画蛇添足)

bring coals to newcastle的用法和样例：

例句

用作不及物动词 (vi.)

1. To argue with such a marl is like beating the air.
   跟这号人辩论是白费力气。
2. He declared it was of no use to work on his farm.
   他对人家说，在自己的田里干活是白费力气。