How much space should you leave when following another vehicle?

Answer: C — At least one car length

It is recommended to maintain at least one car length between you and the vehicle ahead of you when driving. This distance allows you enough time to react in case the other vehicle suddenly stops or slows down. The first option, the length of two cars, may not be enough space in certain situations, such as when driving at higher speeds. Option B, half of a city block, is excessive and may cause traffic congestion. Option D, the length of one car, is not enough space to allow for safe braking distance. Therefore, C, the length of one car, is the most appropriate and commonly recommended distance to maintain when following another vehicle.