Two blocks each of mass m is connected to the spring of spring constant k as shown in the figure. 

If the blocks are displaced slightly in opposite directions and released, they will execute simple harmonic motion. The time period of oscillation is

• A

  $2\mathrm{\pi }\sqrt{\frac{\mathrm{m}}{\mathrm{k}}}$

• B

  $2\mathrm{\pi }\sqrt{\frac{\mathrm{m}}{2\mathrm{k}}}$

• C

  $2\mathrm{\pi }\sqrt{\frac{\mathrm{m}}{4\mathrm{k}}}$

• D

  $2\mathrm{\pi }\sqrt{\frac{2\mathrm{m}}{\mathrm{k}}}$