The above shows isoelectric lines generated by two charged particles and fixed on the -axis of an -plane, where is a positively charged particle. The points and are also on the -axis with the distances from the origin being and respectively. The isoelectric line passing through the point is parallel to the -axis, and the point is on this isoelectric line. Which of the following statements is NOT correct?
a) is a negatively charged particle.
b) The voltage at the point is higher than the voltage at the point .
c) If we put a positive charge on the point , then it does not move.
d) The direction of the electric field at the point is the same as that at the point .