两个固定的等量异种点电荷，在他们连线的垂直平分线上有a、b、c三点，如图所示，若取无穷远处电势ϕ=0，则下列说法正确的是（　　）

A．a点电势比b点电势高

B．a、b、c三点与无穷远处电势相等

C．a、b两点场强方向相同，a点场强比b点大

D．a、c两点场强方向相同，a点场强比c点大

when the dispute over duty payment arises between the duty payer and the Customs, the duty payer should first pay the duty and then, within ______ days of the issuance of the duty memo, apply to the Customs in writing for a reconsidertation of the case.

A．10 days
B．20 days
C．30 days
D．50 days