To prepare for the 2008 Olympic Games, scientists have ________ a number of suggestions to improve the environment．

1. A.
   made up
2. B.
   put forward
3. C.
   applied for
4. D.
   put up

To prepare for the 2008 Olympic Games, scientists have ______ a number of suggestions to improve the environment.

       A. made up                   B. put forward                     C. applied for               D. put up