-Listen! Is Mary playing the piano in the room? --No. It ________ be Mary. She has gone to Hong Kong.
Hurry up, everyone ________ for you.
Trees __________ on Tree Planting Day only.
Sorry, smoking ________ here.
Some rules _________ to stop people from polluting the environment.
I can’t go to the party, because I have to ________ my daughter at home.