与将来事实相反的虚拟语气

请看下面的题目：

If we __________ 200 years old，we __________ everything.

A. were to be，could change B. had been，changed

C. were，would have changed D. should be，changed

此题应选A。该题考查与将来事实相反的虚拟语气，此时的主句谓语通常用would(should，could，might)＋动词原形，而从句谓语可能有以下几种情况：

1. 从句谓语用过去式：

If your father knew this，he would be angry. 要是你父亲知道了，他会生气的。

If it rained tomorrow，the sports meet would beput off. 要是明天下雨，运动会就推迟。

2. 从句谓语用should 动词原形(通常指可能性极小的事情，一般译为“万一”)：

If it should rain，the crops would be saved. 要是有雨，这庄稼还有救。

此类句型的主句谓语有时可以用祈使句甚至将来时态：

If it should rain tomorrow，don’t expect me. 万一明天下雨，就不要等我了。

If I should be free tomorrow，I will come. 万一我明天有空，我就来。

3. 从句谓语用were to 动词原形 (通常指可能性极小可或近乎不可能，有时指出乎意料)：

If the sun were to rise in the west，my love for you would not change. 即使太阳从西边出，我对你的爱也不会变。