21. The U.S. government, according to some reports, immediately formed a special group  to______ the causes of the plane crash.

A. look   through  B.  look   into C. look back  D. look  after

22.Mr. Smith was quite satisfied with his new flat______ beside the West Lake Park and decided to settle down there.

   A. located   B. locating   C. to locate   D. locate

23. ______ this method doesn’t work , let’s try another, OK ?

   A. Since   B. Because  C. As   D. For