[单选题]
An equipotential surf1.-e3xc3jt bt)j 7b wmjpc 6euace.,;bb/n ywce22 akhce must be
A. parallel to the electric field at any point.
B. perpendicular to the electric field at any point.
C. does not exist if the electric field is not uniform.
D. can not exist if the electric field is too strong.
