$A$ massless spring of force constant $K$ is placed between two blocks of masses $m$ and $M$ on a frictionless table and compressed by an amount $x$. Upon releasing the spring,both blocks move in opposite directions. The blocks lose contact with the spring when it reaches its natural length. The speed of the block of mass $M$ at the moment of separation is:

• A
  $\sqrt{\frac{Km}{M(M+m)}} \cdot x$
• B
  $\sqrt{\frac{Km}{m(M+m)}} \cdot x$
• C
  $\sqrt{\frac{KM}{m(M+m)}} \cdot x$
• D
  $\sqrt{\frac{(M+m)K}{m}} \cdot x$