You can watch TV ______, but you can’t watch it ______ a long time.
Now most families have only one child _____ our country’s one-child policy.
There are fifty students in our class, _____ of us _____ football.
Xi’an is a city with many places of interest and _____ tourists come here every year.
.—Which country has the_____population in the world? —China.
—How long have you lived in this town? —_____ 2001.