21. cook, cooker
cook厨师,cooker厨具 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 $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 The police are questioning everyone in the house.