理工类辅导资料：介词用法口诀
do something on the sly （quiet）。秘密地（暗地里，偷偷地）做某事。
I‘ve come here on business. 我是有公事来的。
They went to Bern on a mission. 他们到伯尔尼去执行一项使命。
They has been away on a long trip. 他们出去做一次长途旅行。
I‘ll go home on leave next month. 下月我将休假回家。
I went on business to Shanghai. I did not take leave. 我是公出去上海的，不是不告面别。
She came to see you on purpose.她是专程来看你的。
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）