in
A. Refer to 'time' concept
1.century/dynasty ==> in modern time/in the Han Dynasty
2.year ==> in 2004/in the year of 2008/in the 1930s
3.month ==> She was born in March.
4.season ==> I love to go swimming in summer.
5.a period of time in life ==> I am still in my yeens.
6.in the morning/evening/daytime
7.during a period of time ==> in the past/in the hour of victory.
B. Refer to 'space' concept ==> in the car/park/room
C. directional movement ==> I jump into the river.
Hm, I suggest that you should narrow your question to a specific idea, such as on/in the desk or in the morning/on Monday morning. It would be easier to explain, rather than offering scattered explanation. But I try to compile some for you. Hope that helps. :wink: