If it had rained last night, the ground would be wet now. 要是昨晚下过雨的话，现在地面就会是湿的。
You would be much better now if you had taken my advice. 假若你当时听我的话，你现在就会好多了。
条件从句用 if I were…时，既可指现在也可指过去：
If I were you, I would stay. 我要是你我就会留下。
If I were you, I’d go to night school. 我要是你，我会上夜校。
If I were not busy, I would have come. 假若我不忙，我早就来了。
也可用 if I had been you也表示过去：
If I had been you，I’d have taken the job.