—Hurry up! The bus is coming.—Wait a minute. Don’t cross the street ____________the traffic lights are green.
—It smells terrible. What has happened here? —Look, there is much waste gas _____ from the chemical factory.
—Have you finished your homework? —Not _____. There are still some exercises to be done.
_____ the environment is important for human beings.
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.