1、定語從句中缺主語，修飾人時用who／that，修飾物時用which／that引導。如： Is this the factory which／that makes TV sets？The man who／that visited our school is from Australia．
2、從句中缺賓語，修飾人時用who／whom／that或省略引導詞；修飾物時用which／that或省略引導詞。如：Gone are the days which／that we spent together in the village．He is the man who／whom／that I think to be worthy of our praise.
