He came here on purpose to discuss it with you.

　　他到这来是要与你讨论这件事的。

　　This lunch is on me.

　　"No.let’s go Dutch."

　　"这顿午饭我付钱。"

　　"不，还是各付各的。"

　　On the contrary，it was very easy to understand.

　　相反，这事儿很容易理解。

　　P1ease come on time.(on schedule)

　　请准时来。

　　注：in time是"及时"的意思。

　　The train arrived on schedule.

　　火车准时到达。

　　特定时间和"一……就"，左右on后动名词。

　　例：Gases expand on heating and contract on cooling.

　　气体加热时膨胀，冷却时收缩。(特定时间)

　　On entering the room，he found his friends dancing in high spirits.

　　一进屋，他就发现他的朋友们在愉快地跳舞。

　　On reaching the city he called up Lao Yang.

　　一到城里他就给老杨打了一个电话。

　　I’ll write to him on hearing from you.

　　我接到你的来信就给他写信。(一……就)

　　以及on the left，right向左向右，on the stair在台阶上等。

　　步行、驴、马、玩笑on，cab，carriage用in.

　　例：On foot 步行;on horse骑马;on donkey骑驴。

　　He rode on，blood flowing from his side.

　　他骑着马，鲜血从腰部流下来。