3.

1.we had already prepared the food before the guests arrived.

2. mum had already made breakfast when we got up.

3. Kate had started studying after John leaved.

4. she had realized that she forgot her book at home.

5.Lisa's mother bought her a kitten when she had sung well in the concert the night before.

4.

1. was going/met

2.was/were going

3.wasn't doing/came

4.saw/were playing

5.didn't find/was washing