1 were drinking / came
2 was walking / passed by
3 was thinking / was falling или fell asleep
4 were listening
5 entered / was writing / were copying
6 were getting / began
7 was having
8 came / was doing
9 were doing
10 was going
11 were sleeping / went
12 was reading / came / sat
13 was walking / passed by
14 was looking / saw
15 were answering / entered