Particles of masses $2 M, m$ and $M$ are respectively at points $A, B$ and $C$ with $A B=\frac{1}{2}(B C) . m$ is much-much smaller than $M$ and at time $t=0$, they are all at rest
(a) $m$ will remain at rest
(b) $m$ will move towards $M$
(c) $m$ will move towards $2 M$
(d) $m$ will have oscillatory motion