定语从句在什么情况下只用that 在什么情况下只用which?

根据非限制性定语从句只能由B。如果改成句号，就可用that，用来指前边整个句子．

在下面几种情况下必须用“that”引导定语从句：

1.

当先行词前有一个最高级形容词所修饰时。如：

This

is

one

of

the

most

exciting

football

games

that

I

have

ever

seen.

这是我所看过的足球赛中最激烈的一场。

2.

当先行词前有一个序数词所修饰时。如：

The

first

thing

that

you

could

do

was

to

turn

off

the

light.

你首先要做的就是熄灭灯。

3.

先行词为

all

、

everything

、

nothing

、

something

、

anything

、

little

、

much

、

none

等不定代词时（

something

后也可用

which

）。如：

All

that

we

have

to

do

for

our

students

is

to

tell

them

how

to

speak

English

in

class.

我们为学生所要做的事情就是告诉他们如何在课上说英语。

I'm

going

to

buy

everything

that

I

need.

我要去买我所需要的一切东西。

4.

当先行词前面有

only

、

all

、

any

、

no

等词修饰时。如：

The

only

thing

that

he

could

do

was

to

run

away.

他唯一要做的就是逃跑。

There

are

no

people

that

things

must

not

happen

to.

不碰到事故的人是没有的。

5.当先行词既有人又有物时:

They

talked

of

things

and

persons

that

they

remembered

in

the

school.