Our teacher walked into the classroom _______ a smile _______ his face.
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.