－__________ can you finish your homework, Ben?－ In thirty minutes. 

Food safety is important. Rules____ to stop people from food pollution.

—Why can your neighbor know so much about London?—He ____ have been there before.

—I’m just going to finish the work off first.—Go on if you _______.

— Who’s that man in our classroom? It ________ be Mr. Brown. He is much taller.— You mean the man in white? He is an exchange student from England.