Answer
Average gravitational force, greatest to least: C, A, B.
Work Step by Step
Use the gravity equation, putting in the 2 masses, and the distance between the 2 masses.
$$F_{A}= G \frac{M m}{d^{2}}$$
Note that the sun-moon distance is about the same as the sun-Earth distance, but the moon's mass is only about 1.2% the mass of the Earth. So C $\gt$ B.
The sun-Mars distance is about 1.5 times the sun-earth distance, and Mar's mass is about 11% the mass of the Earth. So C $\gt$ A $\gt$ B.
