[题目]-|||-真空中两块互相平行的无限大均匀带电平面.其电荷密度-|||-分别为 +0 和 +2σ, 两板之间的距离为d,两板间的电场强-|||-度大小为: ()-|||-A.0-|||-B. dfrac (30)(2{varepsilon )_(0)}-|||-C. dfrac (sigma )({varepsilon )_(0)}-|||-D. dfrac (sigma )(2{varepsilon )_(0)}