If you had studied hard before, you would be a college student now.
如果你以前努力学习的话，你现在就是一名大学生了。
主从句谓语动词形式取决于各自要表达的具体时间
含蓄条件句
eg) But for the storm, I would have arrived much earlier.
要不是那场暴雨，我早就到了。
eg) Without your help, I wouldn’t have passed the driving test.
没有你的帮助，我就不会通过驾照考试。
or
otherwise
名词性从句中
宾语从句中
wish后面的宾语从句（通常表示不可能或没有实现的愿望）
eg) I wish I knew everything in the world.
要是我什么都懂就好了。
eg) We wish we had arrived there two hours earlier.
要是我们早到两个小时就好了。
eg) I wish we could go to the seaside someday.
我希望有一天我们能够去海边。
表示现在用过去式
表示过去用过去完成式
表示将来用would,might,could+V原
Disco
They demanded that the black people (should) be treated as well as white people.
他们要求黑人应该和白人一样被同等对待。
一个“坚持”...... insist
两个“命令”...... order/command
三个“建议”...... advise/suggest/propose
四个“要求”...... require/request/demand/desire
would rather
I would rather I hadn’t told him the bad news.
我宁愿没告诉他那个坏消息。
would rather后，从句常用一般过去时形式，表示现在或将来的情况，用过去完成时，表示过去的情况
主语从句中（只做理解，不做掌握）
在句型“It is important(necessary,strange,natural)+that”中，后面谓语动词用should+V原
It is necessary that he (should) listen to the radio frequently.
他很有必要经常听收音机。
在“It is a pity/a shame/no wonder that…”句型中用should+V原
It is a pity that he should fall off his bicycle.
很遗憾，他竟然从自行车上摔下来。
若表示说话人的看法，想法或意见，在句型it is/was+adj.+that从句中，主语从句可用虚拟语气，主语从句中谓语动词用should do表示现在或者将来情况，用should have done表示过去
其他从句中
在as if/though从句中
She treated the pupil as if/as though he were her son.
她对待那个学生就好像他是她的儿子一样。
表示与现在事实相反或对现在情况有所怀疑，as if/though从句谓语用过去式
He looks as if/ as though he had been hit by lighting.
他看起来好像被雷击了。
表示与过去事实相反，as if/though从句谓语用过去完成式
在含有even if/though从句的复合句中
eg) If only I were a flying bird!
要是我是只飞鸟就好了。
eg) If only I had seen the film!
要是我看过这部电影就好了。
若表示与事实相反，可用虚拟语气形式，主从句
谓语形式与非真实条件从句相同
在句型“It is time that(该去做某事)”中，that从句谓语用过去式
It is high time that you went / should go to school.
该是你上学的时候了
