假设条件：如果现在不同，如果当时不同
用时间线理解第二、第三条件句，避免只背公式。
内容更新：
进入本课练习 →这一课学什么
- 与现在不同或较不现实的假设：if + 过去式
- 回想已经发生的过去：if + had done，would have done
与现在不同或较不现实的假设：if + 过去式
If I had more time, I would read more 把拥有更多时间当作假设。这里 had 不一定说过去，而是在当前情境中拉开现实距离。结果部分常用 would + 原形。
If I lived closer, I would walk to school.
如果我住得更近，就会步行上学。
If I were you, I would ask the teacher.
如果我是你，我会问老师。
回想已经发生的过去：if + had done，would have done
If we had left earlier, we would have caught the bus 设想过去采取不同做法的结果。句子暗示实际并没有更早出发，也没赶上那班车。先看两个分句都指过去，再使用这一结构。
If I had checked the address, I would have found the shop.
如果我当时核对了地址，就会找到那家店。
We would have arrived earlier if we had taken the train.
如果当时坐火车，我们就会更早到达。