($A$) The amplitude of oscillation in the first case changes by a factor of $\sqrt{\frac{M}{m+M}}$, whereas in the second case it remains unchanged
($B$) The final time period of oscillation in both the cases is same
($C$) The total energy decreases in both the cases
($D$) The instantaneous speed at $x_0$ of the combined masses decreases in both the cases
$x\left( t \right) = A\,\sin \,\left( {at + \delta } \right)$
$y\left( t \right) = B\,\sin \,\left( {bt} \right)$
Identify the correct match below