On a short trip a driver is more likely to have an accident if there is a passenger in the car, presumably because passengers distract drivers. However, on a long trip a driver is more likely to have an accident if the driver is alone. Which one of the following, if true, most helps to explain the facts described above? ['Good drivers tend to take more long trips than bad drivers.', 'The longer a car trip is, the more likely a passenger is to help the driver maintain alertness.', 'Most drivers take far more short trips than long trips.', 'On a long trip the likelihood of an accident does not increase with each additional passenger.']