选项
A.
A.$E=0$
B.
B.$E=dfrac{lambda L}{4pi epsilon_0 (r^2-L^2/4)}$
C.
C.$E=dfrac{lambda L}{4pi epsilon_0 (r^2-L^2/2)}$
D.
D.$E=dfrac{lambda L}{2pi epsilon_0 (r^2-L^2/4)}$
正确答案：
名词解析
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