一．一般虚拟的构成：(省略if, 要将should/were/had 提到句首)
(1). 对现在的虚拟：If +S.+ did/were sth., S.+ would/could/should +do
If I had time, I would attend the meeting.
If I were you, I would seize the chance to go abroad.
(2) 对过去的虚拟：If +S.+had + p.p, S.+ would/could/should have + p.p
If you had taken my advice, you would not have failed in the exam.
