if表示什么意思的时候用虚拟语气?if和whether怎么区分?

Question

if应该有好几个意思，那么当它表示什么意思的时候句子用虚拟语气?拜托顺便给个例子。 只能用whether的应该有几种情况，麻烦例举一下，谢谢~

Answer 1

在虚拟语气中，没有if
和whether的区分点。(那么在名词性从句中有whether和if的区别要另当别论)。
虚拟语气中if的用法如下:
1.表示对现在的假设:if应到的从句用--did
主句用--would
do
例句:If
i
were
you
,i
should
seize
the
opportunity
to
go
abroad.
2.表示对过去的假设:从句--had
done
主句--would
have
done
例句:If
you
had
taken
my
advice
,you
would
not
have
failed
in
the
exams.
3.表述对将来的假设:从句--did或were
to
do或
should
do
主句--would
do
例句:If
he
should
not
come
tomorrow,we
should
put
off
the
meeting
till
next
Monday.