Today a large coal-fired power plant can give out in a single year as much poisonous gas as was blown out by the May 18,1980 outbreak of Mount St. Helens, ______ some. 400,000 ton.

1. A.
   its amount was
2. B.
   amounts to
3. C.
   amounting to
4. D.
   it was amounted

Today a large coal-fired power plant can give out in a single year as much poisonous gas as was blown out by the May 18,1980 outbreak of Mount St. Helens, ______ some. 400,000 ton. 

A. its amount was  B. amounts to   C. amounting to  D. it was amounted