[单选题]
At a particular instant, an electron moves eastward at speed V in a s14wk kd t,uj9il pkma8 -kau*w,vrs6 oj4( 5runiform mag2db8f-lg th(gnetic field that is dire(g8ld-btgf 2 hcted straight downward. The magnetic force that acts on it is
A. zero.
B. directed upward.
C. directed to the south.
D. directed to the north.
