【单选题】
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<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019043015414860339.jpg?sign=db4c4ff8eec8e7aed5ab910f4914266c&t=62d647f7" />则OXY坐标平面上点（0，a）处的场强<img src="https://nimg.ppkao.com/2019-04/wuacheng/2019043015420295540.jpg?sign=a1f8d24780d94b9b8397c74696d8dea3&t=62d647f7" />为（）<br /> <img src="https://nimg.ppkao.com/2019-04/wuacheng/2019043015421197912.jpg?sign=bbb219c3d344eb3e9dee8ce3558f8c69&t=62d647f7" /><br /> <img src="https://nimg.ppkao.com/2019-04/wuacheng/2019043015422220270.jpg?sign=a1f99ece491c1ccdf0b39a32036d0e1d&t=62d647f7" />
A、A
B、B
C、C
D、D
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