[单选题]
At a particular instant, anh53a h*yr.n1knf 5 sp0 k3wxvq elect+by.qd 2pp7w b,ey0yk ron moves eastward at speed V in a uniform magnetic field that is directed straiye kp yq 72y0bp.db,+wght downward. The magnetic force that acts on it is
A. zero.
B. directed upward.
C. directed to the south.
D. directed to the north.
