The most vexing problem faced by researchers exploring wind-powered generation of electricity is achieving a constant flow of power from an unpredictable natural source that meets demand, but so the flow does not overload electrical grids with sudden voltage increases
A. achieving a constant flow of power from an unpredictable natural source that meets demand, but so the flow does not overload
B. achieving a constant flow of power from an unpredictable natural source, which meets demand but without overloading
C. how to achieve a constant flow of power from an unpredictable natural source, a flow that meets demand but does not overload
D. how to achieve a constant flow of power from an unpredictable natural source, but a flow that meets demand without overloading
E. how a constant flow of power from an unpredictable natural source can be achieved, which meets demand but does not overload
答案是C
弱弱的问D为啥不对呢？
谢谢 | 
