Answer
b) is correct.
Work Step by Step
The net force in the system is composed of the weight of the wine rack $W_r$ and the weight of the bottle $W_b$.
If we choose the axis of rotation to be passing through the point $P$ the rack contacts the tabletop and consider the torques produced by $W_r$ and $W_b$, then because the system is in equilibrium, the net torque is zero: $$\sum\tau=\tau_r+\tau_b=0$$
Now the net torque $\sum\tau=\sum Wx_{cg}$. Because $\sum\tau=0$, if we consider $\sum W$ a single force passing through $x_{cg}$, then it has to pass through the point of the rotation axis, which is $P$, too, so that there is no torque produced. This means $x_{cg}$ and $P$ are connected in a straight line perpendicular to the tabletop, or $x_{cg}$is directly above $P$.
