Answer:
A.) Gravity pulls Neptune towards the sun.
Step-by-step explanation:
Gravity is not the strongest force in nature, actually - it is quite weak in comparison to others.
But it is also the most important force in nature. Gravity is responsible for the formation of the solar system! The sun has more gravity than anything in our solar system! It keeps planets and other small bodies in a continous and elliptical orbit. The same applies to Neptune!
Also, did you know that the mass of the sun makes up 99.8% of ALL the mass in our solar system? That's pretty cool, right?