Final answer:
The idea that a force is required for an object to continue moving at a constant velocity was refuted by Galileo, who showed that objects retain their velocity unless acted upon by a force. This principle was later incorporated into Newton's first law of motion. The correct answer b. Galileo.
Step-by-step explanation:
The belief that a force is necessary for motion to continue at constant velocity was actually refuted by Galileo Galilei.
Contrary to the accepted Aristotelian hypothesis that objects 'naturally' slow down and stop unless a force acts upon them, Galileo concluded that objects retain their velocity unless a force, often friction, acts upon them.
This principle was later incorporated into Newton's first law of motion, which states that an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force. Therefore, the correct answer to the student's question is b. Galileo.