----- __________it be Li Ping who broke the glass?---- No. It __________ be Wu Dong who did it.

We ___have hurried all the way to the airport—the flight was called off because of the foggy weather. 

—How’s your tour around the North Lake? Is it beautiful?—It          be, but it is now heavily polluted.

       you be interested, I’ll tell you the whole story.

This nationwide smog should serve as a reminder to all, indicating a high time that we ______ on what we've done to the environment.