一、通常情况
1. “主将从现”见于时间状语从句
As soon as I get through with my work I’ll join you. 我工作一做完就来找你们。
As soon as my divorce goes through, we’ll get married. 一俟我的离婚申请获准，我们就结婚。
Before they drive any of the buses, they will have to pass a special test. 然而在驾驶公共汽车前,他们必须通过专门测验。
My mother will be very angry with me when she finds out where I’ve been. 我母亲要是知道我到过那地方一定会大怒。
We’ll pay you half up front and the other half when you’ve finished the job. 我们先付给你一半钱，剩下的一半等你干完了再付。
2. “主将从现”见于条件状语从句
If (it is) necessary I will come at 6. 如有必要，我6点钟来。
If today is Wednesday, the day after tomorrow will be Friday. 今天要是星期三，后天就是星期五。
If you train hard, you’ll make a good footballer. 你要刻苦训练就能成为优秀的足球运动员。
If you add too much liquid the mixture will not be thick enough. 加入的液体太多，混合液的浓度就不够。
If past experience is anything to go by, the plane will be late. 过去的经验要是还靠得住的话，这飞机会晚点的。