A cubical region of space is filled with some uniform electric and magnetic fields . An electron enters the cube magnetic fields. An electron enters the cube across one of its faces with velocity $\overrightarrow {v}$ and a position enters via opposite face with velocity - $\overrightarrow v$ At this instant .

Question

$\begin{array}{1 1} \text{the magnetic forces on both the particle cause equal accleration } \\ \text{both particles gain or loose energy at the rate} \\ \text{the motion of the center of mass(M) is determined by $\overrightarrow{B}$ alone} \\ \text{all the above} \end{array}$