A person with a type B lipid profile is at much greater risk of heart disease than a person with a type A lipid profile. In an experiment, both type A volunteers and type B volunteers were put on a low-fat diet. The cholesterol levels of the type B volunteers soon dropped substantially, although their lipid profiles were unchanged. The type A volunteers, however, showed no benefit from the diet, and 40 percent of them actually shifted to type B profiles. If the information above is true, which one of the following must also be true? ['The reduction in cholesterol levels in the volunteers is solely responsible for the change in their lipid profiles.', 'Apart from adopting the low-fat diet, most of the volunteers did not substantially change any aspect of their lifestyle that would have affected their cholesterol levels or lipid profiles.', 'For at least some of the volunteers in the experiment, the risk of heart disease increased after having been put on the low-fat diet.', 'In the experiment, most of the volunteers had their risk of heart disease reduced at least marginally as a result of having been put on the diet.']