An electron is launched with velocity \[\vec{v}\] in a uniform magnetic field\[\vec{B}\]. The angle \[\theta \] between \[\vec{v}\] and \[\vec{B}\] lies between 0 and\[\pi /2\]. Its velocity vector \[\vec{v}\] returns to its initial value in a time interval of

• A. \[\frac{2\pi m}{eB}\]     
• B. \[\frac{2\times 2\pi m}{eB}\]
• C. \[\frac{\pi m}{eB}\]       
• D. Depends upon angle between \[\vec{v}\] and \[\vec{B}\]