8. 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[spoiler]（D）[/spoiler]
(E) are either now or will be within a few years 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[spoiler]（D）[/spoiler]
(E) are either now or will be within a few years economically competitive with conventional sources of heat and power
