定语从句中一定要用that的9种情况是什么？？

没有九种,就有几种.
如:表示物时:I like music that is quiet.
表示人时:I prefer friends who are easygoing.
、 既这个从句起的作用与形容词完全一样，起修饰和限定主句里名词的作用。可以形容人，物和事件，在主句中充当定语的作用。试比较：

1． I like quiet music.

2． I like music that is quiet.

二、 定语从句中的关系代词

1． 指人：who / whom

2． 指物：that / which

三、 关系代词在从句中的作用

1． 充当从句里的宾语

eg. He is the man who (whom/that) I met.

= ( I met ) the man

I love music that ( which ) I can dance to.

= ( I can dance to ) music

2． 充当从句里的主语

I prefer friends who are easygoing.

= friends

I can’t stand music that are too loud.

= music