Cars play an important role in modern life, but they ______ also cause many problems like air pollution. 

—Miss Li, must we hand in our homework right now?—No, you ____.You can hand it in tomorrow.

—     you play the piano at this time of the day ? I need a good rest for tomorrow’s test. — Sorry.  

The new supermarket announced that the first to purchase goods on the opening day_______ get a big prize.

The boy is afraid of darkness, so he _____ out at night.