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  3. There is evidence that the usual variety of high blood pressure is, in part, a family disease. Since families have similar genes

There is evidence that the usual variety of high blood pressure is, in part, a family disease. Since families have similar genes

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问题     There is evidence that the usual variety of high blood pressure is, in part, a family disease. Since families have similar genes as well as similar environment, family diseases could be due to shared genetic influences, to shared environmental factors, or to both. For some years, the role of one’s environmental factor commonly shared by families, namely, dietary salt, has been studied at Brookhaven National Laboratory. These studies suggest that chronic excess salt ingestion can lead to high blood pressure in man and animals. Some individuals, however, and some rats consume large amounts of salt without developing high blood pressure. No matter how strictly all environmental factors were controlled in these experiments, some salt - fed animals never develop hypertension whereas  a few rapidly developed very severe hypertension followed by early death. These marked variations were interpreted to result from differences in genetic constitution.
    By mating in successive generations only those animals that failed to develop hypertension from salt ingestion, a resistant strain (the" R" strain) has been evolved in which consumption of large quantities of salt fails to influence the blood pressure significantly. In contrast, by mating only animals  that quickly develop hypertension from salt, a sensitive strain ("S" strain) has also been developed.
    The availability of these two strains permits investigations not heretofore possible. They provide a plausible laboratory model on which to investigate some clinical aspects of the human proto - types of hypertension. More important, there might be the possibility of developing methods by which genetic susceptibility of human beings to high blood pressure can be defined without waiting for its appearance.
In the experiments, ______.
选项 A、there was an increase in the human consumption of salt
B、salt -eaters have bad health conditions
C、the environment was strictly monitored
D、high -blood pressure was easier put under control
答案C
解析 文中所述的实验中，没有证明ABD，只有C提到，控制环境因素，才能研究遗传与salt对高血压的影响，答案是C。
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