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 haemorrhage, caused when a brain artery busts. The report suggests that because blood cholesterol plays a vita 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 haemorrhage than do non-Western diets.

The argument is based on which one of the following assumption?

[A]. Western diets are healthier than non-Western diets.
[B]. Western diets result in higher blood cholesterol levels than do non-Western diets.
[C]. High blood cholesterol levels preclude the weakening of artery walls.
[D]. Cerebral haemorrhages are more dangerous than strokes caused by blood clots.
[E]. People who have low blood pressure are at increased risk of cerebral haemorrhage.
Answer: B

According to a recent report, low blood cholesterol weakens artery walls, increasing the likelihood that the arteries will rupture, and thereby bring about a cerebral hemorrhage. The author concludes that this new report supports the long-held belief of Japanese researchers that Western diets are better at protecting against cerebral hemorrhage than are non-Western diets. For this conclusion to be valid, the author must be assuming that Western diets lead to a higher blood cholesterol level than non-Western diets.

(A) A healthier diet isn’t the issue here—we need information that fills in the connection between the blood cholesterol evidence and the conclusion of the Japanese researchers in the last sentence, and this isn’t it.

(C) The author tells us that high blood cholesterol lowers the risk of weakened artery walls. He never says that it eliminates this risk, nor does his argument depend on this information.

(D) is an irrelevant comparison. In fact, the author could assume that cerebral haemorrhages are less dangerous than strokes caused by blood clots, and it wouldn’t damage his claim that Western diets are less likely to lead to cerebral haemorrhages.

(E) involves a scope shift: Low blood pressure is an irrelevant issue, because we don’t know how this relates to blood cholesterol.

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