If you don’t know how to use the word you should in a dictionary.A. look up itB. look it

问题补充：

If you don’t know how to use the word, you should in a dictionary.

A. look up it

B. look it up

C. look them up

D. look up them

答案：

A. look up it

(答案→)B. look it up

C. look them up

D. look up them

解析：it它，指代前文提到过的单数事物；them他们，指代前文提到过的复数名词；句意：如果你不知道如何用这个单词，你应该在词典里面查一下。英语中当人称代词做由动词+副词构成的动词短语的宾语时，应该放在动词后面，副词前面。本句中代词指代前文提到的单数名词word，故选B。