题目选项分析

The most vexing problem faced by researchers exploring wind-powered generation of electricity is how to achieve a constant flow of power from an unpredictable natural source, a flow that meets demand but does not overload electrical grids with sudden voltage increases.

The most vexing problem faced by researchers exploring wind-powered generation of electricity is how to achieve a constant flow of power from an unpredictable natural source, but a flow that meets demand without overloading electrical grids with sudden voltage increases.