Why is gravity acting on a rock falling to the ground considered an unbalanced force?

Question

Because gravity is balanced by air resistance, causing the rock to fall at a constant speed.

Because gravity is the only force acting on the rock, causing to accelerate towards the ground.

Because gravity is opposed by an equal and opposite force, keeping the rock in motion.

Because gravity is the only force acting on the rock, causing it to stay at rest.

Answer 1

The correct answer is:

Because gravity is the only force acting on the rock, causing it to accelerate towards the ground.