补充题96. (420) There is substantial evidence that certain forms of solar energy either now or within a few years will be economically competitive with conventional sources of heat and power. (A) either now or within a few years will be economically competitive with conventional sources of heat and power (B) will either be economically competitive with conventional sources of heat and power within a few years or are so now (C) will be economically competitive with conventional sources of heat and power either now or within a few years (D) either are now economically competitive with conventional sources of heat and power or will be so within a few years（D） (E) are either now or will be within a few years economically competitive with conventional sources of heat and power D和E有什么区别? | 
