求指导本题解题过程，谢谢您！13.图中所示为一沿X轴放置的"无限长"分段均匀带电直线,电荷线密度分别为-|||-+lambda (xlt 0) 和 -lambda (xgt 0), 则OXY坐标平面上点(0,a)处的场强E为[ ]-|||-(A)0 B) dfrac (lambda )(2pi {varepsilon )_(0)a}overline (i) Y-|||-(0,a)-|||-(C) dfrac (lambda )(4pi {varepsilon )_(0)a}i (D) dfrac (lambda )(4pi {varepsilon )_(0)a}(overrightarrow (i)+overrightarrow (j)) +λ λ

求指导本题解题过程，谢谢您！