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
25. man, a man
man人类;
a man一个男人 eg:Man will conquer nature.
26. chick, chicken
二者均可指小鸡;
chicken还可以当鸡肉 eg:The chicken is delicious.
27. telegram, telegraph
当电报解时，telegram指具体的;
telegraph指抽象的 eg:a telegram, by telegraph
28. trip, journey, travel, voyage
travel是最常用的;
trip指短期的旅途;
journey指稍长的旅途;
voyage指海上航行 eg:a three-day trip