There is a widespread belief among the science world ____ we keep on _____  the earth as we are doing today,

the exist ence of us humans on this planet will be out of the question in some years yet to come.[ ]

A. if; polluting

B. if; to pollute

C. that if; to pollute

D. that if; polluting

不变资本和可变资本的划分依据是______。