高收入群体和低收入群体是两个独立的决策主体，各自决定是否接受这个环保项目，并根据效用最大化原则做出有利于自身的最优决策。

A.The high-income and low-income groups are two separate decision-makers.They decide whether they will accept the environmental protection project on their own and make optimum decisions for themselves according to the principle of maximum utility.

B.The high-income group and the low-income group are two independent decision-makers.They decide whether to accept the environmental protection project or not， and make the best decision for themselves according to the principle of maximum utility.

C.High-income groups and low-income groups are two independent decision-making bodies， each of which decides whether to accept this environmental protection project and make optimal decisions that are beneficial to themselves according to the principle of utility maximization.

D.The high-income group and the low-income group are two independent decision-making subjects.They decide whether to accept this environmental protection project or not and make the best decision for themselves according to the principle of utility maximization.

正确答案：The high-income and low-income groups are two separate decision-makers.They decide whether they will accept the environmental protection project on their own and make optimum decisions for themselves according to the principle of maximum utility.