only if引导什么从句

　　Only if the red light comes on is there any danger to employees.

　　只有红灯闪亮时才有危及职工的险情。

　　Children are admitted only if accompanied by an adult.

　　儿童必须有成年人陪同方可入场。

　　I'll do that, but only if we set a few rules.

　　我可以干，但我们得定几条规矩。

　　You can make progress only if you are modest.

　　惟虚心乃能进步。

　　The medicine works only if taken for a long time.

　　此药久服方见功。

　　I'll go only if you go with me.

　　除非你跟我去，我才去。

　　One can grasp a foreign language only if he studies hard.

　　唯有努力学习，才能掌握外语。