The policemen are in uniform.警察們穿著統(tǒng)一制服.
be in uniform.固定搭配“穿制服,”
uniform是集合名詞,我從沒見過用復(fù)數(shù)的情況.一般用于特定的一類人.那如果改成The policemen wearuniform對，可以的。例如：We must wear uniform every day.我們必須每天穿校服。為什么也不加s，這也是固定詞組嗎，那他校服的復(fù)數(shù)用在哪里的啊呵呵，我剛剛看了一下。uniform指制服，是個可數(shù)名詞，但有時卻是不可數(shù)名詞，例如in uniform就是不可數(shù)的，‘他穿著校服’是He is in school uniform，‘他們穿著校服’同樣是They are in school uniform。而wear uniform則可不可數(shù)都可以，你可說They wear uniforms，也可說They wear uniform。一般而言，uniform是可數(shù)的，例如：He is wearing a new school uniform, which sits badly on him（他穿的新校服并不合身）。