Unit 91
IF YOU'RE CONFUSED BY ALL the news about the health effects of eating fish, you're not alone. On one hand, the omega-3 fatty acids in fish are known to reduce the risk of heart disease, as the American Heart Association reminded us two weeks ago when it restated its recommendation that everybody eat at least two fish servings a week. On the other hand, fish that feed in contaminated waterways contain high levels of mercury, which can lead to cognitive problems in developing brains. That's why pregnant women and nursing mothers are advised to limit their consumption.
As if that weren't confusing enough, two new studies published last week in the New England Journal of Medicine investigated the possible effects of mercury on the heart, and they seem to have reached contradictory conclusions. One found no clear link between mercury levels and heart disease; the other found that men with high levels of mercury in their toenails were more likely to suffer a heart attack than those with low levels. What are we to make of this? The first thing to remember is that this is how science proceeds, by fits and starts and seemingly contradictory results that get resolved only by further study. The second is that not all fish are created equal.
Compared with all the other things you might eat, fish are an excellent source of protein. They tend to eat algae as part of their natural life cycle, converting it into omega-3 fatty acids that can improve your cholesterol profile. But it's also true that our waterways have become increasingly contaminated with all sorts of pollutants, including mercury, and that these pollutants tend to accumulate at different levels in different species. The fish most at risk are predators high in the pelagic food chain, such as swordfish and sharks （see chart）.
It was to test the effects of mercury on the heart that the two new studies compared the mercury levels in clippings from toenails, where heavy metals tend to be deposited. In one study, researchers led by Dr. Eliseo Guallar at Johns Hopkins found that European and Israeli men with the highest mercury levels were nearly 2.2 times as likely to have a heart attack as those with the lowest levels. The other study, led by Dr. Walter Willett at the Harvard School of Public Health, looked at a selection of American men and found no connection between mercury exposure and risk of heart disease, although Willett told me a "weak association" cannot be ruled out.
For most of us, eating two servings of fish a week should not pose any problems. Guallar, who hails from coastal Spain, continues to flavor his paella with salmon, which has negligible mercury levels. Willett eats swordfish only about twice a month——because of its expense, not any fear of mercury. Fish-oil supplements are high in omega3 fatty acids and probably don't contain as much mercury as whole fish. But they don't taste nearly as good.
注（１）：本文选自Time; 12/9/2002, p99；
注（２）：本文习题命题模仿对象2005真题Text 1；
1. In the opening paragraph, the author introduces his topic by
[A]making a comparison
[B]justifying an assumption
[C]posing a contrast
[D]explaining a phenomenon
2. The phrase “by fits and starts”（Line 6, Paragraph 2） most probably means _______.
[A]something happens smoothly
[B]something keeps starting and then stopping again
[C]something deserves a lot of effort
[D]something is troublesome
3. Clippings from toenails were chosen for the research most probably because _______.
[A]they are more likely to contain mercury
[B]they influence a person's heart
[C]they can be easily obtained
[D]they are connected with the heart
4. The views of Dr. Eliseo Guallar and Dr. Walter Willett are ______.
[A]identical
[B]similar
[C]opposite
[D]complementary
5. What can we infer from the last paragraph?
[A]Fish is no threat to Man.
[B]Do not be frightened by some fish.
[C]Eat Fish-oil supplements instead of fish.
[D]Taste is more important than the safety of the food.
答案：CBACB
篇章剖析
本文采用提出问题——分析问题的模式，指出吃鱼对心脏有好处，但是其中所含的汞却对心脏有害，二者该做如何取舍。第一段指出人们对吃鱼对健康究竟有无影响、有何影响这一问题感到困惑；第二段以两项新课题为例，进一步说明人们的这一困惑；第三段指出鱼类自身所具有的优点及其存在的一些潜在的危险；第四段详细介绍这两类新课题的研究发现；第五段间接指出我们该做如何取舍。
词汇注释
omega-3 fatty acids n.（不饱和）脂肪酸
contaminate [kEn5tAmIneIt]v.污染
by fits and starts adv.间歇地, 一阵一阵地
algae [5AldVi:]n.藻类, 海藻
at risk有危险
predator [5predEtE（r）]n.掠夺者, 食肉动物
pelagic [pI5lAdVIk]adj.远洋的, 浮游的
swordfish [5sC:dfIF]n.[鱼] 旗鱼
rule out v.划去, 排除, 取消
hail from v.来自
paella [pB:5elE] n （西班牙）肉菜饭
negligible [5neg^IdVIb（E）l]adj.可以忽略的, 不予重视的
难句突破
It was to test the effects of mercury on the heart that the two new studies compared the mercury levels in clippings from toenails, where heavy metals tend to be deposited.
主体句式：It was … that…
结构分析：本句是强调句型。判断是否是强调句型的办法是把“It was … that…”去掉，看是否还是一个完整的句子。
句子译文：脚趾甲是重金属最易于沉积的地方。这两个新课题通过对比脚趾甲中汞的含量的多少，目的在于检测汞对心脏的影响。
题目分析
1.答案为C,属事实细节题。在引入论题时，作者在第一段用了一个词组：on one hand…on the other hand，意思是“一方面．．．另一方面”，就吃鱼与否引出两种完全不同的观点，从而导致很多人就此问题感到困惑。
２．答案为B,属猜词题。习语by fits and starts所在语境“The first thing to remember is that this is how science proceeds, by fits and starts and seemingly contradictory results that get resolved only by further study.”。从此句我们可看出科学的进程并不是一蹴而就。此题我们可考虑使用排除法做出选择。
３．答案为A，属推理判断题。原文对应信息是“It was to test the effects of mercury on the heart that the two new studies compared the mercury levels in clippings from toenails, where heavy metals tend to be deposited.”做好本题的关键是对此句的理解。
４．答案为C，属事实细节题。Dr. Eliseo Guallar和Dr. Walter Willett做的实验相似，但是得出的结论却完全不同。
5．答案为B，属推理判断题。原文对应信息是“For most of us, eating two servings of fish a week should not pose any problems.” 然后，作者又给出了两个例子来进一步说明这一观点。
参考译文
如果吃鱼对人体健康方面有所影响的报道令你感到困惑的话，那么有你这种感觉的并不单单是你一个人。一方面，美国心脏学会两周前再次建议大家每人每周至少吃两回鱼，他们是这样提醒我们的：鱼肉中所含的不饱和脂肪酸可以降低心脏病的发病率。另一方面，生长于污染水域的鱼体内存有高含量的汞，这可能对发育中的大脑造成认知方面的不良影响。这就是为什么要建议孕妇和哺乳期妇女减少鱼类摄入的原因。
这好象还不足以使你感到困惑不解。上周刊载于新英格兰医学杂志上的两项新课题，就汞对心脏可能造成的影响进行了调查研究，两项研究却得出了似乎相互矛盾的结论：一项研究发现汞含量和心脏病之间没有必然联系；另一项研究发现脚趾甲中汞含量高的人与汞含量低的人相比，更容易患心脏病。我们该如何理解？首先要牢记这就是科学的进程，那些时进时退并且看起来相互矛盾的结论只能通过进一步的研究才能得以解决；其次，所有的鱼类并不是天生都一样的。
与其它我们可食用的东西相比，鱼类是蛋白质的最佳来源。它们把吃食海藻作为自然界生命循环的一部分，并将其转化为能促进胆固醇代谢的不饱和脂肪酸。但是我们越来越多的水源被各种污染物（其中包括贡）所污染这也是事实，这些污染物在不同的生物体内以不同程度的含量积聚下来。最危险的鱼是处于海洋上层食物链中最高级的食肉鱼，比如旗鱼和鲨鱼（见图表）。
脚趾甲是重金属最易于沉积的地方。这两个新课题通过对比脚趾甲中汞的含量的多少，目的在于检测汞对心脏的影响。其中一个课题的研究员由约翰霍普金斯大学的Eliseo Guallar博士带领，他们发现在欧洲人和以色列人当中，体内汞含量较高的人犯心脏病的几率几乎为汞含量较低的人的2.2倍。另一项课题由哈佛公共卫生学院的Walter Willett博士牵头。通过对那些选出来的美国男性公民的研究，他们并未发现人体接触汞元素和心脏病发病之间有什么关系，虽然Willett说不能完全排除其中会有某种“微弱的联系”。
对于我们大多数人来说，一周吃两份鱼类食品不会产生任何问题。鲑鱼中汞的含量可以忽略不计。来自西班牙海岸的Guallar继续在他吃的肉菜饭里加鲑鱼调味。Willett每月只吃两回旗鱼——这是因为旗鱼太贵，而不是因为担心汞含量的问题。鱼油补充品富含不饱和脂肪酸，其中所含的汞元素可能也没有整鱼那么多，但它们的口感实在太差。
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