Food safety is important. Rules to stop people from food pollution.
---Someone is knocking at the door. Who may it be?---It ______ be Tom. He is still in the school.
Lucy had few close friends. So she didn’t know ________ about the trouble.
Her singing lessons her five hours a week.
He can’t state clearly how long he has ___________ the bicycle?
----How can I improve(提高) my listening skills?-----_______________more.