beat the air; fish in the air; plough the air; plough the sand

1. 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.
2. 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.
3. 過去的事哭也是白費力氣。
   It is no use crying about the past.
4. 在無人島上夸耀富有也是白費力氣。
   It is of no use boasting of being rich on a desert island.
5. 這都是毫無作用的。告訴你，你是在白費力氣。
   It's all to no purpose. I tell you that you are ploughing the sand.

白費的英語翻譯：

力的英語翻譯：