A portion is fired from origin with velocity `vec(v) = v_(0) hat(j)+ v_(0) hat(k)` in a uniform magnetic field `vec(B) = B_(0) hat(j)`. In the subsequent motion of the proton
A. its Z co-ordinate can never be negative
B. its x co-ordinate can never be positive
C. its x and z co-ordinates cannot be zero at the same time
D. its y co-ordinate will be proportional to its time of flight
