A spring elongated by length 'L' when a mass 'M' is suspended to it. Now a tiny mass 'm' is attached and then released, its time period of oscillation is -

Question

( A ) $2\pi \sqrt{\frac{Ml}{(m+M)g}}$
( B ) $2\pi \sqrt{\frac{ml}{mg}}$
( C ) $2\pi {\sqrt \frac{(M+m)l}{Mg}}$
( D ) $2\pi \sqrt{L/g}$