It is hard for me to imagine what I would be doing today if I had not fallen in love at the age of seven, with the Melinda Cox Library in my hometown.(虚拟的主将从现）
Grace doesn't want to move to New York because she thinks if she were to live there, she wouldn't be able to see her parents very often.
Sorry, I am too busy now. If I had time, I would certainly go for and outing with you. (主过将从过）
The weather has been very hot and dry. - Yes. If it had rained even a drop, things would be much better now! And my vegetables wouldn't have died. （主过将完， 从过完）
If my car had been more reliable, I would have driven to Lhasa instead of flying last summer.（主过将完， 从过完）
Had I known(=if I had known) about this computer program, a huge amount of time and energy would have been saved. (主过将完， 从过完)