Ex1:
B. Was listening
C. Studied
D. Was preparing
E. Was meeting
F. Were painting
G. Called
H. Were swimming
I. Were playing
Ex 2:
A. Was doing, came
B. Was sitting, were playing
C. Fell
D. Were driving, were listening
E. Was, rang
F. Was cleaning, fell
G. Were making
H. Was going, met
I. Were dancing, went
Ex 3:
B. When
C. When
D. When
E. When
F. While
