Answer:
The gravitational force between m₁ and m₂, is approximately 1.06789 × 10⁻⁶ N
Explanation:
The details of the given masses having gravitational attractive force between them are;
m₁ = 20 kg, r₁ = 10 cm = 0.1 m, m₂ = 50 kg, and r₂ = 15 cm = 0.15 m
The gravitational force between m₁ and m₂ is given by Newton's Law of gravitation as follows;

Where;
F = The gravitational force between m₁ and m₂
G = The universal gravitational constant = 6.67430 × 10⁻¹¹ N·m²/kg²
r₂ = 0.1 m + 0.15 m = 0.25 m
Therefore, we have;

The gravitational force between m₁ and m₂, F ≈ 1.06789 × 10⁻⁶ N
Based on the law of conservation of energy, we know that we can't create energy, machines can only convert one type of energy into another. So, if we want to improve a machines's ability then we need to reduce it's loss energy (part of energy which is useless). Out of all the options only Option C fits best with it.
In short, Your Answer would be Option C
Hope this helps!
I believe it is “runs on parallel circuits”! my bad if incorrect
I can't draw you the graph right now because i'm out but look up graphing calculator and click on the first one, type in your equation and it will show you the graph
Net force can be defined as the sum of force acting on an object in all the directions
.i.e Net force= F acting on a body at upward direction+ F at downward direction+ F at leftward direction+ F at rightward direction.
e.g if a body is at rest the sum of forces acting on body in all direction is zero
but if a body is moving its mean body is facing an unbalanced net force.