具体你可以参考这一段。
when,while,as引导时间状语从句的区别
when,while,as显然都可以引导时间状语从句,但用法区别非常大。
一、when可以和延续性动词连用,也可以和短暂性动词连用;而while和as只能和延续性动词连用。
①
Why
do
you
want
a
new
job
when
youve
got
such
a
good
one
already?(get为短暂性动词)你已经找到如此好的工作,为何还想再找新的?
②Sorry,I
was
out
when
you
called
me.(call为短暂性动词)对不起,你打电话时我刚好外出了。
③Strike
while
the
iron
is
hot.(is为延续性动词,表示一种持续的状态)趁热打铁。
④
The
students
took
notes
as
they
listened.(listen为延续性动词)学生们边听课边做笔记。
二、when从句的谓语动词可以在主句谓语动作之前、之后或同时发生;while和as从句的谓语动作必须是和主句谓语动作同时发生。
1.从句动作在主句动作前发生,只用
when。
①When
he
had
finished
his
homework,he
took
a
short
rest.(finished先发生)当他完成作业后,他休息了一会儿。
②When
I
got
to
the
airport,the
guests
had
left.(got
to后发生)当我赶到飞机场时,客人们已经离开了。
2.从句动作和主句动作同时发生,且从句动作为延续性动词时,when,while,as都可使用。
①When
/While
/As
we
were
dancing,a
stranger
came
in.(dance为延续性动词)当我们跳舞时,一位陌生人走了进来。
②When
/While
/As
she
was
making
a
phonecall,I
was
writing
a
letter.(make为延续性动词)当她在打电话时,我正在写信。
3.当主句、从句动作同时进行,从句动作的时间概念淡化,而主要表示主句动作发生的背景或条件时,只能用
as。这时,as常表示“随着……”;“一边……,一边……”之意。
①
As
the
time
went
on,the
weather
got
worse.(as表示“随着……”之意)
②
The
atmosphere
gets
thinner
and
thinner
as
the
height
increases.随着高度的增加,大气越来越稀薄。
③As
years
go
by,China
is
getting
stronger
and
richer.随着时间一年一年过去,中国变得越来越富强了。
④The
little
girls
sang
as
they
went.小姑娘们一边走,一边唱。
⑤The
sad
mother
sat
on
the
roadside,shouting
as
she
was
crying.伤心的妈妈坐在路边,边哭边叫。
4.在将来时从句中,常用when,且从句须用一般时代替将来时。
①You
shall
borrow
the
book
when
I
have
finished
reading
it.在我读完这本书后,你可以借阅。
②When
the
manager
comes
here
for
a
visit
next
week,Ill
talk
with
him
about
this.下周,经理来这参观时,我会和他谈谈此事。
三、when用于表示“一……就……”的句型中(指过去的事情)。
sb.had
hardly(=scarcely)
done
sth.when...=Hardly
/
Scarcely
had
sb.done
sth.when...
①I
had
hardly
/scarcely
closed
my
eyes
when
someone
knocked
at
the
door.=Hardly
/
Scarcely
had
I
closed
my
eyes
when
someone
knocked
at
the
door.我刚一闭上眼,就有人在敲门了。
②I
had
hardly
/scarcely
entered
my
room
when
the
telephone
rang.=Hardly
/Scarcely
had
I
entered
my
room
when
the
telephone
rang.我刚一走进房门,电话就响了。
left,when引导的时间状语从句,主句用一般过去时,从句也用一般过去时
连词when, before, after, if引导的状语从句要特别注意其时态。
1.当主句的谓语动词是一般将来时时,从句要用一般现在时。如:
The boy will be a writer when he grows up.这个男孩长大后将成为一名作家。
I won’t go to school if it rains tomorrow.如果明天下雨我就不去学校。
2.主句的谓语动词是情态动词+动词原形时,从句的谓语动词也用一般现在时。如:
When the lights are red, the traffic must stop.红灯亮时,车辆必须停下。
3.主句是祈使句时,从句也要用一般现在时。如:
Please don’t go to bed before you finish your homework.在完成作业之前,请不要休息。
4.主句谓语用一般过去时时,从句也要用一般过去时。如:
They talked about the party after people left.人们离开后,他们谈论这次晚会情况。
在if、unless等词引导的条件状语从句,when、till/until、as soon as、the time等词引导的时间状语从句,以及the more...the more结构引导的程度状语从句中,当主句中的动词用一般将来时,从句中的动词通常用一般现在时表示将来时间。有时,也可以在从句中用现在完成时表示将来某一时刻前已完成的动作。
时间状语从句:
连接时间状语从句的连接词有:
(1)
连词:when,
while,
as.
它们都表示当…时候的意思。如果主句和从句的动作同时发生且都是进行时
态,只用while,
as.
其他情况下when,
while,
as通用。
1
When
he
came
in,
I
was
listening
to
the
radio.
2
As
I
was
wandering
in
the
street,
I
met
her.
3
While
(as)
I
was
watching
TV,
my
mum
was
cooking
in
the
kitchen.
(2)
连词before,
after,
since,
until(till).
当他们表示时间时,他们既是介词又是连词。
{
He
usually
drinks
a
cup
of
tea
before
he
goes
to
school.
连词
He
usually
drinks
a
cup
of
tea
before
going
to
school.
介词
{
He
usually
drinks
a
cup
of
coffee
after
he
comes
back
from
school.
连词
He
usually
drinks
a
cup
of
coffee
after
coming
back
from
school.
介词
{
I
have
lived
in
Dalian
since
my
son
was
born
in
1999.
连词
通常情况下,主句用现在完成时,从句用一般过去时。
I
have
lived
in
Dalian
since
1999.
介词
{
I
will
wait
here
until(till)
you
finish
your
job.
连词
I
will
wait
here
until(till)
8pm.
介词
(3)
词组:as
soon
as
{
I
will
tell
him
as
soon
as
he
comes
back.
As
soon
as
she
finishes
her
homework,
she
will
play
tennis.
通常情况下,主句用一般将来时,as
soon
as
引导的从句用一般现在时。
如何确定时间状语从句的时态
可以从主句判断
一般是和主句保持一致的
但是也有例外
比如:主句一般将来时,时间状语从句一般现在时
had left
前面已经是过去时了,从句当然是过去的过去了。