________ such heavy pollution already, it may now be too late to clean up the river．

1. A.
   Having suffered
2. B.
   Suffering
3. C.
   To suffer
4. D.
   Suffered

_____such heavy pollution already, it may now be too late to clean up the river.

A.  Having suffered     B. Suffering    C. To suffer     D. Suffered

_______ such heavy pollution already, it may now be too late to clean up the river.

A. Having suffered   B. Suffering  C. To suffer                           D. Suffered

________ such heavy pollution already, it may now be too late to clean up the river.

A. Having suffered　　 B. Suffering

C. To suffer　　　 　D. Suffered

________ such heavy pollution already, it may now be too late to clean up the river.

A. Having suffered B. Suffering 　　　 C. To suffer 　　　 D. Suffered