3)与将来事实相反的虚拟:
(1) If should v., ... would v.
(可能性很小)(译作“万一”)
If it should rain tomorrow, you could stay at home.
If I should fail, what should Ido?
(2) If did / were to v ..., would v.
(完全不可能)
If the sun were to rise in the west, I would lend you the money.
If you finished it in 3 minutes, I would give you my car.