21. cook, cooker

cook厨师;
cooker厨具 eg:He is a good cook.

22. damage, damages

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

23. police, policeman

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

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