A person' s dietary consumption of cholesterol and fat is one of the most important factors determining the level of cholesterol in the person' s blood (serum cholesterol). Serum cholesterol levels rise proportionally to increased cholesterol and fat consumption until that consumption reaches a threshold, but once consumption of these substances exceeds that threshold, serum cholesterol levels rise only gradually, even with dramatic increases in consumption. The threshold is one fourth the consumption level of cholesterol and fat in today' s average North American diet. The statements above, if true, most strongly support which one of the following? ['People who consume half as much cholesterol and fat as in the average North American diet will not necessarily have half the average serum cholesterol level.', 'Serum cholesterol levels cannot be affected by nondietary modifications in behavior, such as exercising more or smoking less.', 'People who consume less cholesterol and fat than the threshold cannot reduce their serum cholesterol levels.', 'People who consume an average North American diet cannot increase their consumption of cholesterol and fat without dramatically increasing their serum cholesterol levels.']