-
情态动词
+
动词完成时
,
即情态动词
+have+done.
表示对过去的行为或动作进行
推测
,
评
论或者判断
.
have
done.
表示对过去某事的肯定猜测，其否定或疑问形式
都用
can/could
来表示。
例如：
since the
road is wet,it must have rained last night.
2
；当然对现在发生或者将来发生的
事情，要用
must
do
表示猜测，否定为
can?t
do
he must
understand that we mean business.
you must be hungry after a long walk.
反意疑问句中含有
Must
的情况主要有以下几种：
1
）作为情态动词表
“
必须
”
，这时反意疑问句直
接用
mustn'/needn't
2)
当
must
表示推测时又分以下
几种情况：
a
：对现在事实的推测，反意疑问句与
must
后面的动词呼
应，如
:
You must be
joking,aren't you ?
b:
对过去事实的推测，
表示动作的时候用
did <
/p>
当助动词，
表示状态时用
was
，
如：
Mr Green must have been punished for
his being rude at the
meeting
，
didn?t
he
?(
格林先生一定因为昨天在会上鲁莽的行为被处罚了，是吗？）
被处罚表示
一个动作
She must have been a
policeman ,wasn't she
?
（她过去一定是个警察，
是吗？）
是警察表示一种状态
对现在情况的推测，问句部分用主动词（
do,be)
一般现在时的适当形式。若是现
在进行时，问
句部分用现在进行时的适当形式表示。若是
there be
结
构，问句
用
isn't/aren't
there
。如：
1)He must be there,isn't he?
2)He must have a big
family,doesn't he?
3)He
must be waiting outside,isn't he?
4)There must be some students in the
room,aren't there?
对已发生的过去情况的推测，若陈述句谓语部分有
“must
have done”
，而且有表
示过去的时间状语，问句部分
用
didn't
；若没有表示过去的时间状语，问句部分
用
haven't
或
hasn't
。如：
1)They must have gone there last
night,didn't they?
2)They
must have arrived by now,haven't
they?
（根据
by
now
来判断）
3)They must have been to the Great
Wall,haven't they?
若是被动，应按被动结构来处理。如：
1)The room must have been
cleaned yesterday,wasn't it?
2)The room must have been
cleaned,hasn't it?
若句中有表示过去完成时的时间状语，问句部分应用
hadn't.
如
:
They
must have learnt 5000 English words by the end of
last term,hadn't they?
(
本题中
must
表推测，如果将它去掉，还原
为真实句就是
They
had
learnt
5000
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