3.与将来事实可能相反的假设

若表示某事将来实现的可能性不大，则条件状语从句中用“should+动词原形”，也可用“were to+动词原形”或用动词的过去式，主句中用“would/should/could/might+动词原形”。

If it should rain/were to rain/rained，we wouldn't go out．

如果下雨，我们就不出去了。

If we were to panic，we would not be able to help．(人教大纲版高二上第59页)

如果我们慌了手脚，那就帮不上忙了。

If these numbers were to grow，the future of Africa might be in danger．(人教大纲版高二上第127页)

如果这些数字增大的话，非洲的未来就很危险了。