Tom made a few friends in China and he __________them by e-mail last year.A. keeps in touch withB. keeps up withC.kept in touch with
—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.