The greater the number of people who regularly use a product, the greater the number whose health is potentially at risk due to that product. More people regularly use household maintenance products such as cleaning agents and lawn chemicals than regularly use prescription medicines. Ttherefore, it is even more important for such household products to be carefully tested to ensure their safety than it is for prescription medicines to be so tested. Which one of the following principles, if valid, most helps to justify drawing the conclusion in the argument above? ['The more people whose health might be at risk from the regular use of a particular product, the more important it is for that product to be carefully tested to ensure its safety.', 'It is very important for any product that is regularly used by a large number of people to be carefully tested to ensure its safety.', 'If one type of medicine must be taken in more frequent doses than another type of medicine, it is more important for the former to be carefully tested than for the latter.', "It is generally more important for a medicine than it is for a nonmedical product to be carefully tested to ensure its safety unless more people's health would be at risk from the nonmedical product than from the medicine."]