A Spherical hole of radius $\large\frac{R}{2}$ is made in a solid sphere of radius R. The mass of the sphere before hollowing was M. The gravitational field at the center of the hole due to the remaining mass is

Question

$a)\; zero \\b)\;\frac{GM}{2 R^2} \\c)\;\large\frac{GM}{8R^2}\\ d)\;\frac{GM}{R^2}$