1. Don’t wear jeans, or ______ won’t be allowed to go to the concert.

  A. I             B. you                C. we             D. they

2. Our teacher often warns us _____ the street when the traffic light is red.

  A. to cross       B. not cross            C. crossing         D. not to cross

3. With the development of transportation, CRH trains are used ______ more and more people ______ traveling.

  A. by; by        B. by; for              C. for; by          D. for; for