Question

______ is a natural force that causes a vehicle to increase speed going downhill.
reaction
gravity
perception

Explanation:

To solve this, we analyze each option:

• "Reaction" refers to a response, not a force causing speed increase downhill.
• "Gravity" is a natural force that pulls objects towards the Earth's center. When a vehicle is going downhill, gravity acts to accelerate it (increase its speed).
• "Perception" is about how we interpret sensory information, not a force related to speed.

So the correct option is the one related to the force causing downhill speed increase.

Answer:

B. Gravity