3.
1) was riding
2) saw
3) thought
4) was moving
5) tried
6) tried (was trying)
7) followed
8) saw
9) was walking
4.
1 He was studying, when the phone rang.
2 I was reading the newspaper while John was washing the car.
3 We were jogging in the park, when I lost my wallet.
4 My brother was surfing the Net while I was talking on the phone.