good turn

He once did her a good turn, but she repaid it with a bad turn.

他曾经帮助过她, 而她却以怨报德。

At the very least, I figure maybe a few good turns on the exercycle will keep me from snacking before I hit the buffet table.

我算计着多踩几自行车至少能帮助我在吃自助餐前不去动小吃了。