Resposta:
1. I ( was making) dinner when he arrived.
2. At 7 o'clock, Mom (was baking) a cake.
3. When I arrived ( was taking) a shower.
4. Jim sent me a message this morning while I (was waiting) for the bus.
5. She (was mowing) the grass when the phone rang?
Explicação:
to be no passado pode ser Was ou Were
e o verbo ao lado é adicionado "ing"