白費力氣的用法和樣例：
例句
-
大夏天推銷大衣真是白費力氣。
Trying to sell overcoats in midsummer is a real mug's game. -
他白費力氣想抓住停在花上的蝴蝶。
He tried in vain to catch the butterfly on the flower. -
過去的事哭也是白費力氣。
It is no use crying about the past. -
在無人島上誇耀富有也是白費力氣。
It is of no use boasting of being rich on a desert island.
