The variables and affect the gravitational force between objects.
a) weight, mass
b) volume, weight
c) distance, mass
d) rotation, distance

The correct option is (c) distance, mass.    

Explanation :

According to the universal law of gravitation, the forces acting between two objects in the universe is given by :

........(1)

Where,

F is the gravitational force between two objects.

G is universal gravitational constant.

and are masses of two objects.

d is the distance between two objects.

From equation (1) it is clear that the gravitational force between objects depends only on the masses and the distance between objects.

So, the variables distance and mass affect the gravitational force between objects.