Answer:
Option C, The square of the distance that separates them
Step-by-step explanation:
The formula for gravitational pull between two objects is given by

Where
G = gravitational constant

m1 and m2 is the mass of the two objects
and r is the distance between the two objects
Thus, as visible from the equation,
Gravitational force "F" is directly proportional to mass of the bodies and inversely proportional to the square of the distance that separates them
Thus, option C is correct.