ANS:B - Newton's third law of motion.

The propulsion of a rocket primarily follows from Newton's third law of motion. Newton's third law states that "for every action, there is an equal and opposite reaction." In the context of rocket propulsion, this means that as the rocket expels mass (propellant) out of its engines at high speed in one direction (action), there is a corresponding force pushing the rocket in the opposite direction (reaction). This is known as the reaction force or thrust, which propels the rocket forward. In simple terms, the rocket pushes the exhaust gases backward, and in return, the exhaust gases push the rocket forward. This is the fundamental principle behind how rockets generate thrust and achieve propulsion in space.