An Proton Travels Through a Region of Space with No

An proton travels through a region of space with no acceleration. Which one of the following statements is the best conclusion?

A) Both E and B must be zero in that region.
B) E must be zero, but B might be non-zero in that region.
C) E and B might both be non-zero, but they must be mutually perpendicular.
D) B must be zero, but E might be non-zero in that region.
E) E and B might both be non-zero, but they must point in opposite directions.