根据句意从方框中选择合适的动词,并用其适当时态填空。
I was reading a book while my mother ___________.
Mary often __________ shopping on weekends when she was at primary school.
Didn’t your teacher tell you that sound ________ more slowly than light?
If everyone can take action to protect the environment, the world _______ more beautiful.
I won’t go to see the film tonight, because I __________ my ticket.