[单选题]
An electron has an initial vj* k3qnqtn.s6r cp 5d1m.nt 0delocitr q9 f( t2qv7brc6gr/zy to the south but is observed to curve upward as the result of g6t q7f 9v(c/b2zrrrq a magnetic field. The direction of the magnetic field is
A. to the west.
B. to the east.
C. upward.
D. downward.
