Question

An asteroid leaves our solar system and continues moving in the same direction at the same speed for millions of years. What allows the asteroid to keep moving?

A. Friction
B. Force
C. Inertia
D. Acceleration

Answer 1

C. Inertia.

Remember, I provided you a definition of inertia in one of your earlier questions:
"Inertia is the resistance of any physical object to any change in its motion (including a change in direction). In other words, it is the tendency of objects to keep moving in a straight line at constant linear velocity."

This goes along with Newton's first law of motion:
"An object at rest stays at rest and an object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force."

Answer 2

yes.. since the resistance acted on the asteroid are air molucules..