Topic: Rigid Bodies
Concepts: Moments of inertia, Rolling down inclined plane

Solution:

Recall the acceleration $a$ of an object rolling without slipping down an incline of angle $\theta$ is

where the object has moment of inertia $I=\beta mr^2$. We will find the effective $\beta$ for our composite object of a spherical shell containing a frictionless fluid. Since the shell and fluid both have mass $M$, this object has mass $2M$. A frictionless fluid does not have rotational inertia so only the shell contributes to the moment of inertia $I=\frac{2}{3}MR^2$. Thus,

so the answer is B.