Ответ:

1)walked, noticed

2)were they, had

3)was working, was playing

4) happened, got, brushed, prepared, was eating, screamed, got, found, was

5)were you doing, was writing

6)was studying, came

7)were lying

8)were cooking, rung

9)saw, passed

10)was having, arrived

11)was waiting, spotted

12)got, discovered, were leaking, was

13)gave

14)were singing, were cycling

15)were swimming,appeared