无逗号即限 eg:Do you know the man who spoke just now?(限制性定语从句)
有逗号非限 eg:He has a brother , who works in Guiyang.(非限制性定语从句)
随着先行变 (先行：即所被的指人或指物有先行词 )
who;whom要当先 eg:We know the students (who/that are very naughty in our school).
which;that两出现 eg:The jacket (which/that is hanging on the wall) is mine.
缺定用whose eg:This is the girl (whose family is in the northeast.)
缺主用who;that eg: All architect is a person (who/that) designs house and buidings.
Which把物接 eg:Please bring back the dictionary (which/that) I lent you last week.
缺宾找who;whom;that eg:The doctor (who/whom/that)we are talking about can speak French.
通常可省略 eg:The person (whom/who) I spoke to just now is our teacher
只许which;whom接 eg:The teacher for whom you are waiting is coming.
且不可省略 eg: This is the book to which I referred in my talk.
who;whom两可兼 eg:His father , whom he loved dearly , died last year.
that滚一边 eg:He has a sister , who works in Shanghai is called Liping.
which独得天 eg: I have read the book A Tale of Two Cities , which was written by Charles Dikens.
用when来当填 eg.He came last night when I was out
where字必须选 eg.The place where I met her was railway station
用why合因原 eg.The reason why he didn’t go to school yesterday is that he was very sick..
用how永不变 eg.This is the way how he worked out the problem.