A recent study of 10, 000 people who were involved in automobile accidents found that a low percentage of those driving large automobiles at the time of their accidents were injured, but a high percentage of those who were driving small automobiles at the time of their accidents were injured. Thus, one is less likely to be injured in an automobile accident if one drives a large car rather than a small car. Which one of the following, if true, most seriously weakens the argument? ['Most people who own small cars also drive large cars on occasion.', 'Only a small percentage of those people involved in an automobile accident are injured as a result.', 'Half of the study participants drove mediumsized cars at the time of their accidents.', 'A large automobile is far more likely to be involved in an accident than is a small automobile.']