The public is well aware that high blood cholesterol levels raise the risk of stroke caused by blood clots. But a recent report concludes that people with low blood cholesterol levels are at increased risk of the other lethal type of stroke -- cerebral hemorrhage, caused when a brain artery bursts. The report suggests that because blood cholesterol plays a vital role in maintaining cell membranes, low blood cholesterol weakens artery walls, making them prone to rupture. The conclusion thus supports a long-standing contention by Japanese researchers that Western diets better protect against cerebral hemorrhage than do non-Western diets. The argument is based on which one of the following assumptions? ['High blood cholesterol levels preclude the weakening of artery walls.', 'Cerebral hemorrhages are more dangerous than strokes caused by blood clots.', 'Western diets result in higher blood cholesterol levels than do non-Western diets.', 'People who have low blood pressure are at increased risk of cerebral hemorrhage.']