[单选题]
At a particular instant, an electron moves eastward at speed V in a uni 9ug orpmi29r+cmyb 13form mag3c z3odv9.n wqtv6es7netic field that is directo6dw3 9.qncz3esvt7 ved 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.
