A particle of mass m and charge q enters a region of magnetic field (as shown) with speed v. There is a region in which the magnetic field is absent, as shown. The particle after entering the region collides elastically with a rigid wall. Time after which the velocity of particle becomes antiparallel to its initial velocity is

• A. \[\frac{m}{2qB}(\pi +4)\]
• B. \[\frac{m}{qB}(\pi +2)\]
• C. \[\frac{m}{4qB}(\pi +2)\]
• D. \[\frac{m}{4qB}(2\pi +3)\]