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

　　我可以干，但我們得定幾條規(guī)矩。

　　You can make progress only if you are modest.

　　惟虛心乃能進步。

　　The medicine works only if taken for a long time.

　　此藥久服方見功。

　　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.

　　唯有努力學習，才能掌握外語。