Final answer:
Gravity causes acceleration because it exerts a force on all objects, resulting in a downward acceleration towards Earth's center, with a constant value of approximately 9.80 m/s².
Step-by-step explanation:
The reason that gravity causes acceleration is because gravity exerts a force on all objects. According to Newton's second law of motion, any force will cause an object to accelerate in the direction of the force. Since gravity is a force that acts towards the center of the Earth, it causes any object that is free from other forces such as friction or air resistance to accelerate towards the Earth at a constant acceleration known as acceleration due to gravity, which is approximately 9.80 m/s². This acceleration applies to all objects in free-fall and allows us to use kinematics equations to describe their motion.
In summary, the correct answer to the student's question is: A) Gravity exerts a force on all objects, causing acceleration.