21. He missed the plane ______ driving very fast to the airport.
A. despite     B. unless           C. if        D. without 
22. After the fire, very little of the house ________ standing.
   A. left        B. remained        C. rested     D. held
23. I’m sure your suggestion will ____ the problem.
   A. contribute to solve       B. be contributed to solve
   C. contribute to solving     D. be contributed to solving