--Why does the river smell terrible?

--Because large quantities of water__________.

A. have polluted                   B. is being polluted

C. has been polluted        D. have been polluted

-Why does the river smell terrible?

--Because large quantities of water__________.

A. have polluted                   B. is being polluted

C. has been polluted        D. have been polluted

--Why does the river smell terrible?

--Because large quantities of water__________.

 ---Why does the river smell terrible?

   ---Because large quantities of water          .

   A．have polluted      B．is being polluted  C．has been polluted   D．have been polluted

--Why does the river smell terrible?
--Because large quantities of water__________.