An electron moving with a speed u along the positive x-axis at `y=0` enters a region of uniform magnetic field which exists to the right of y-axis. The electron exits from the region after some time with the speed v at coordinate y, then
A. `vgtu, ylt0`
B. `v=u, ygt0`
C. `vgtu,ygt0`
D. `v=u,ylt0`