19.   Black Americans are, on the whole, about twice as likely as White Americans to develop high blood pressure. This likelihood also holds for westernized Black Africans when compared to White Africans.

Researchers have hypothesized that this predisposition in westernized Blacks may reflect an interaction between western high-salt diets and genes that adapted to an environmental scarcity of salt.

Which of the following statements about present-day, westernized Black Africans, if true, would most tend to confirm the researchers’ hypothesis?

(A) The blood pressures of those descended from peoples situated throughout their history in Senegal and Gambia, where salt was always available, are low.

(B) The unusually high salt consumption in certain areas of Africa represents a serious health problem.

(C) Because of their blood pressure levels, most White Africans have markedly decreased their salt consumption.

(D) Blood pressures are low among the Yoruba, who, throughout their history, have been situated far inland from sources of sea salt and far south of Saharan salt mines.

(E) No significant differences in salt metabolism have been found between those people who have had salt available throughout their history and those who have not.
答案是A，我选了D。看了以前大家的讨论，天哪，连解释也没看懂，5555。

为什么非A--->非B是加强呢？从来没听说过也？

试着解释一下：

文章说，黑人容易得高血压，说是两种原因得相互作用：1.环境是高盐得。2.基因里是适应缺盐的。

换句话说：本来是适应低盐环境的，现在一吃很多盐的食物，就高血压了

A：环境高盐的，（吃很多盐的食物），到了欧洲血压就低。

D：环境低盐的，（吃很多盐的食物），到了欧洲血压就低。－－－错

首先，原文说低盐的祖先的后代，在高盐的当今环境容易得高血压。说明盐的

多少导致了基因，导致了今天的状况。问加强

A 是说，有这么一拨人，原来生存的环境是高盐的，所以现在血压就低。可以这么

理解，取非以后，原来生存的高盐的环境的黑人，到了现在血压还是高。就说明不

是盐的关系导致高血压，直接推翻了原文。

能理解不？

是这样

作者推理链是这样的

因为黑人的基因是适应低盐的，现在一到欧洲，食物都是高盐的，所以容易得高血压

即，原先基因是适应低盐环境得－－－高盐环境－－得高血压

A：where salt was always available是一个非限制型定语从句修饰得SG，

即SG是个不缺盐得地方，在那里出来得人的基因是适应高盐环境的，基因到了高盐得环境，不得高血压。

加强

D：一个远离海洋的地方的内陆地区出来的人，适应了低盐环境，这样的话，其基因也是适应低盐的，根据文章，适应低盐的人，出来后，到了欧洲，应该是容易得高血压，可选项得现在式说是低，所以是不符合文章得意思得。

总算弄明白了。这要是在考试中，3分钟我也没法搞定，难题。不过还好答案

是A，以后只好难题猜A了。

谢谢各位楼主的帮忙。