______ environmental damage is done, it takes many years for the ecosystem to recover.

A. Even if          B. If only           C. While            D. Once

_______environmental damage is done, it takes many years for the ecosystem to recover.

1. A.
   Even if
2. B.
   If only
3. C.
   While
4. D.
   Once

 _______ environmental damage is done, it takes many years for the ecosystem to recover.

A. Even if                       B. If only                      C. While                       D. Once

 ________ environmental damage is done , it takes many years for the ecosystem to recover .

   A. Even if   B. while   C. If only   D. Once

______ environmental damage is done, it takes many years for the ecosystem to recover.

A. Even if　 B. If only　 C. While　　 D. Once