N1
1 is flowing
2 complain
3 walk
4 borrow
N2
1 began
2 had
3 took
4 worked
N3
1 was eating
2 was hurrying
3 were preparing
4 was arguing
N4
1 found
2 was reading
3 was playing
4 fell
N5
1 has studied
2 has dropped
3 has rained
4 have had
N6
1 bigger
2 most difficult
3 better (well)