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.