look them up还是look it up

1、单复数要看前后文,这个应该不会难倒你的
2、如果后面是单就It,反之用them
再问： 是不是既可以是a word 也可以是words?
再答： 是的： 1You'd batter look it up in a dictionary when you see a new word. 2You'd batter look them up in a dictionary when you see new words.