A certain medication that is frequently prescribed to lower a patient' s cholesterol level is generally effective. A recent study of 1, 000 subjects ranging widely in age indicates, however, that the cholesterol level of someone taking the medication is typically 12 to 15 percent higher than the average for that person' s age group. Which one of the following, if true, most helps to explain how both of the claims made above could be true? ['The medication described above is usually prescribed only for people whose cholesterol level is at least 30 percent above the average for their age group.', 'Another medication is prescribed to treat high cholesterol just as often as the medication described above is.', 'Within the population as a whole, approximately the same number of people have relatively high cholesterol levels as have relatively low cholesterol levels.', 'A recently developed cholesterol-lowering medication is more effective than the medication described above.']