An electron moving with a speed $u$ along the $+ve\: x$ - axis and at $y = 0$ enters a region of uniform magnetic field $\overrightarrow B = -B_0 \hat k $ after sometime with speed $v$ at co-ordinate $ y$, then which exists to the right of the $ y$ - axis. The electron exits from the region

Question

$\begin {array} {1 1} (a)\;v > u, y < 0 & \quad (b)\;v > u, y > 0 \\ (c)\;v = u, y > 0 & \quad (d)\;v = u, y < 0 \end {array}$