An ideal spring with spring constant.k is hung from the ceiling and a block of mass M is attached to its lower end. The mass is released with the spring
initially unscratched. Then the maximum extension in the spring is

• A

  $4\mathrm{Mg}/\mathrm{k}$

• B

  2 Mg/k

• C

  Mg/k

• D

  Mg/2k