In a region of space, a uniform magnetic field \( B \) exists in th...

In a region of space, a uniform magnetic field \( B \) exists in the \( y \)-direction. A proton is fired from the origin, with its initial velocity v making a small angle \( \alpha \) with the \( y \)-direction in the yz plane. In the subsequent motion of the proton,
(A) its x-coordinate can never be positive
(B) its \( x- \) and \( z \)-coordinates cannot both be zero at the same time
(C) its z-coordinate can never be negative