[单选题]
An equipotential surfacl bq8(7ixs/tiq 0i sd gk,rqot+4 w5l-q,)xdwe must bc9 -4ynvfk px )ynl)z)e
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.
