in(在……里)

　　She was born in 1980.

　　We’ll be back in three days.

　　( He came back three days ago.)

　　Do you work in the daytime or at night?

　　We’ll be back in no time. (in no time 立刻，马上)

　　He is in his early thirties. (in one’s thirties 三十多岁)

　　He is always in a good mood.

　　(in a good mood 情绪很好 in a bad mood 情绪很糟)

　　I have no difficulty/ trouble in solving the problem.

　　(no difficulty in doing sth. 没有困难)

　　Did you have any difficulty in finding the hotel?

　　Can you write in English?

　　They have done it in a wrong way. (in a wrong way 错误的方式)

　　They accepted the plan in principle. (in principle 原则上)