A proton moving in a region of a space does not experience any acceleration in t

A proton moving in a region of a space does not experience any acceleration in the direction of motion. Which of the following statements is correct with respect to this situation?
A) The electric and magnetic fields must be perpendicular to each other in that region.
B) The electric and magnetic fields must be parallel to each other in that region.
C) Both electric and magnetic fields must be zero in that region.
D) The electric field must be zero but not the magnetic field in that region.
E) The magnetic field must be zero but not the electric field in that region.