–Look! A man is cutting a tree on the moon. --It ______ be true. The teacher said there is no air on the moon.
Xi’an is a city with many places of interest and __ tourists come here every year.
—_____ you _____ your homework yet? —Yes, I _____ it ten minutes ago.
It’s necessary for you _____ exercise every day.
—I _______ here since I was five years old.
The Greens _____ China for seven years.