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看到一个 老美的解释挺好的 you need to pick a choice that actually points out a salient difference, regarding prostate cancer, between the two countries.
furthermore, that difference must register in the correct direction: i.e., the evidence must indicate that prostate cancer is LESS likely to be found in terland.
choice (c) does no such thing. in fact, choice (c) is perfectly neutral, giving absolutely no reason to suspect different levels of prostate cancer in the two countries. (first, "does not increase one's risk" implies equality of risk, not a disparity in either direction. second, this statement has absolutely no bearing whatsoever on differences between the two countries mentioned in the problem.)
choice (b), on the other hand, mentions a factor that is DIRECTLY responsible for the relatively low rate of prostate cancer in terland.
namely, if people in terland don't live long enough to GET prostate cancer in the first place, then you aren't going to see a lot of prostate cancer there. and there you have it.
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by the way, this problem is an exact analogue of the real-world situation with such maladies as heart disease and breast/prostate cancer, which generally strike older individuals.
there are often strikingly low rates of death from those maladies in countries with otherwise horrible public health (such as sub-saharan african countries). this isn't due to better prostate/heart/breast health in those countries, though; it's simply because most people in those countries don't live anywhere near long enough to get these problems in the first place. | 
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发表于 2009-8-4 19:43:00
