–Look! The man at the gate ____ be our headmaster. He is always standing there every morning.-- No, it _____ be him. He is holding a meeting in the office now.
Drinking too much ____ your health.
These are plastic bags. Don’t ____.
There are usually ____ people in the supermarket every weekend.
Do you know how to ____ ice into water?
Let’s try our best to ____ paper to save the trees.