The T-shirts are half price. Why not __________?
This is the most beautiful park I have _____ visited.
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.