--What is the model plane like?

--Well, the wings of the plane are___________ of its body.

A．more than the length twice

B．twice more than the length

C．more than twice the length

D．more twice than the length

地面水自净作用中最重要和最活跃的净化是

A．物理净化过程
B．化学净化过程
C．物理化学净化过程
D．生物净化过程
E．微生物净化过程