With more forests being destroyed, huge quantities of good earth __________ each year, which __________ that our environment is suffering.

A．are washing away, suggest

B．is being washed away, suggest

C．have been washed away, suggests

D．are being washed away, suggests

50gNaNO₂溶于水并稀释至250ml，则此溶液的质量浓度是（）

A.50g／L

B.100g／L

C.200g／L

D.250g／L

E.25g／L