1、表示与现在事实相反的情况:
从句:
If
主语+过去时
主句:
主语+should/would/could/might+do
eg:
1.If
I
were
you,I
would
take
an
umbrella.
如果我是你,我会带把伞。(事实:我不可能是你)
2.If
I
knew
his
telephone
number,I
would
tell
you.
如果我知道他的电话号码,我就会告诉你。(事实:不知道)
3.If
there
were
no
air
or
water,there
wou