#1
a) was digging / saw
b) was looking / turned on
#2
a) They (are) were playing
b) when we (were meeting) met him
#3
a) Не was having breakfast when
I arrived
b) Tim was doing his homework at 5 o'clock yesterday.
#4
a) We were sleeping when our neighbours turned on the radio.
b) When the teacher asked the question, Sasha was talking