There is evidence that the usual variety of high blood pressure is, in part, a
familial disease. Since families have similar genes as well as similar
environment, familial diseases could be due to shared genetic influences, to
shared environmental factors, or to both. For some years, the role of one
environmental factor commonly shared by families, namely dietary salt, has been
studied at Brook-haven National Laboratory. These studies suggest that chronic
excess salt ingestion (摄政) 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 (高血压) whereas a few rapidly developed very severe hypertensions
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 (the S strain) has also been
developed. The availability of these two strains permits
investigations not therefore possible. They provide a plausible laboratory model
On which to investigate some clinical aspects of the human developing methods by
which genetic susceptibility (敏感性) of human beings to high blood pressure can be
defined without waiting for its appearance.
单选题
The main idea of this passage is ______.
A. genetic constitution, or hereditary factor is all important factor that
may underlie hypertension
B. Excessive use of salt may cause high blood pressure
C. Shared environmental factors may lead to familial disease
D. There are two different kinds of strains in animals which cause their
different reactions to excess salt ingestion
【正确答案】
A
【答案解析】[解析] 根据第一段前两句话“There is evidence that the usual variety of high blood pressure is, in part, a familial disease. Since families have similar genes as well as similar environment, familial diseases could be due to shared genetic influences, to shared environmental factors, or to both.”可知，有证据证明，在某种程度上，高血压是一种家族性疾病，因为家人有相似的基因，生活在相似的环境中，所以家族性疾病可归因于有共同的基因影响，共同的环境因素，或者两者都有，文章接着从遗传方面分析盐的摄入量与高血压的关系，所以选A。
单选题
The study made by Brook-haven National Laboratory shows ______.
A. Shared environmental factors can cause hypertension
B. Dietary salt can lead to high blood pressure in man and animals
C. Some rats not some individuals do not develop high blood pressure by
consuming large amounts of salt
D. High blood pressure can be developed as a result of too much consumption
of dietary salt
【正确答案】
D
【答案解析】[解析] 根据第一段第四句话“These studies suggest that chronic excess salt ingestion (摄取) can lead to high blood pressure in man and animals.”可知，这些研究表明，长期过量食用食盐可能导致人和动物的高血压，所以选D。
单选题
The main difference between the "R" strain and the "S" strain lies in
their ______.
A. quantities of salt consumed
B. Choice of mating partner
C. blood pressure
D. Reaction to salt
【正确答案】
D
【答案解析】[解析] 根据第二段可知，两个例子的作用在于对比动物对不同盐量的反应。
单选题
In the second sentence of the last paragraph, the word "they" refers
______.
A. Scientists engaged in the experiments
B. Investigations made by people
C. The resistant strain and the sensitive strain
D. The availability of the two strains
【正确答案】
C
【答案解析】[解析] 根据上下文，上一句表明they可能指the two strains，也可能指investigations，但下句则排除了指代investigations的可能性。
单选题
What can you infer from the passage?
A. The experiments show that salt ingestion does not necessarily cause
animals to develop by pretension with the environmental factors being
equal.
B. Dietary salt is harmful to human being's health.
C. Human beings' high blood pressure will never be easily put under
control.
D. In order not to develop hypertension, man should consume chemically pure
salt.