What leads to hydroplaning?

Answer: C — Water buildup under the tires

Hydroplaning occurs when a layer of water builds up between the tires of a vehicle and the surface of the road, causing the car to lose contact with the road and potentially skid or slide. This can happen in wet or rainy conditions, and can be worsened by excessive speed (as option B mentions) or aggressive braking (as option D mentions). Low tire pressure (option A) can also contribute to hydroplaning, as it reduces the amount of traction the tires have on the road. However, it is primarily water buildup under the tires (option C) that causes hydroplaning.