1. act as [充当；担任]
[构成]:act[行动] + as[作为]
例句：He will act as the manager during her absence. [她不在时他将担任经理。]
2. act out [将...表演出来；付诸行动]
[构成]:act[行动] + out[出来]
例句：The children acted out the story. [孩子们把这个故事表演了出来。]
3. act up [捣蛋；出毛病]
[构成]:act[行动] + up[向上]
例句：The car is acting up again. [这辆车又出毛病了。]
4. in the act of [正在做...时]
[构成]:in[在...里] + the[定冠词] + act[行动] + of[关于]
例句：I caught him in the act of stealing. [我在他偷东西时当场抓住了他。]
5. act for [代理；代表]
[构成]:act[行动] + for[为了]
例句：I'm acting for my boss while he's on vacation. [老板度假时我代理他。]
6. put on an act [装模作样]
[构成]:put on[穿上；上演] + an[一个] + act[表演]
例句：Don't put on an act. Just be yourself. [别装模作样了，做你自己就行。]
7. act upon [对...起作用；按照...行动]
[构成]:act[行动] + upon[在...上]
例句：You should act upon my advice. [你应该按照我的建议行动。]
8. act of kindness [善举]
[构成]:act[行动] + of[关于] + kindness[善良]
例句：A simple act of kindness can make someone's day. [一个简单的善举可以让某人的一天变得美好。]
9. act of violence [暴力行为]
[构成]:act[行动] + of[关于] + violence[暴力]
例句：We condemn any act of violence. [我们谴责任何暴力行为。]
10. act of God [天灾；不可抗力]
[构成]:act[行动] + of[关于] + God[上帝]
例句：The insurance doesn't cover damage caused by an act of God. [保险不包括天灾造成的损害。]
11. a clean act [诚实的行为]
[构成]:a[一个] + clean[干净的；诚实的] + act[行为]
例句：His behavior was a clean act. [他的行为是诚实的。]
12. an heroic act [英勇行为]
[构成]:an[一个] + heroic[英勇的] + act[行为]
例句：His sacrifice was an heroic act. [他的牺牲是一种英勇行为。]
13. a rash act [轻率的行为]
[构成]:a[一个] + rash[轻率的] + act[行为]
例句：It was a rash act to quit the job without thinking. [不加思考就辞职是个轻率的行为。]
14. a criminal act [犯罪行为]
[构成]:a[一个] + criminal[犯罪的] + act[行为]
例句：Stealing is a criminal act. [偷窃是犯罪行为。]
15. a noble act [高尚的行为]
[构成]:a[一个] + noble[高尚的] + act[行为]
例句：Helping the poor is a noble act. [帮助穷人是高尚的行为。]
16. an evil act [恶行]
[构成]:an[一个] + evil[邪恶的] + act[行为]
例句：His betrayal was an evil act. [他的背叛是恶行。]
17. a brave act [勇敢的行为]
[构成]:a[一个] + brave[勇敢的] + act[行为]
例句：Fighting for justice was a brave act. [为正义而战是勇敢的行为。]
18. a foolish act [愚蠢的行为]
[构成]:a[一个] + foolish[愚蠢的] + act[行为]
例句：Investing all your money in that project was a foolish act. [把你所有的钱都投资在那个项目上是愚蠢的行为。]
19. a kind act [善良的行为]
[构成]:a[一个] + kind[善良的] + act[行为]
例句：Giving a helping hand is a kind act. [伸出援手是善良的行为。]
20. a generous act [慷慨的行为]
[构成]:a[一个] + generous[慷慨的] + act[行为]
例句：Donating a large sum of money to charity was a generous act. [向慈善机构捐赠一大笔钱是慷慨的行为。]