21. cook, cooker

cook 厨师，例：He is a good cook.
cooker 厨具。

22. damage, damages

damage 不可数名词，损害，损失；
damages 复数形式，赔偿金，例：$900 damages

23. police, policeman

police 警察的总称，后接复数谓语动词，例：The police are questioning everyone in the house.
policeman 指某个具体的警察。

24. problem, question

problem 常和困难连系，前面的动词常为think about, solve, raise；
question 常和疑问连系，多和ask, answer连用。

25. man, a man

man 人类；
a man 一个男人，例：Man will conquer nature.