--There is somebody knocking at the door. Who________ it be?--I’m not sure. It ________ be a postman.
You won’t feel happy at school ________ you get on well with your classmates.
I ________ my homework, I guess I can’t join you.
We have a lovely room. It’s one of ________ in the hotel.
---We must act now because time is ________. --- Yes, Let’s start.
They were ________ busy ________ with each other ________ the time.