Blood pressure usually falls in warm weather.（)

ase. 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.

Which statement relates the main idea of this passage？

A．When salt is added to their diets, rats and men react in much the same way.

B．The near future will see a cure for high blood pressure.

C．Modem research has shown that high blood pressure is a result of salt in the diet.

D．A tendency toward high blood pressure may be a hereditary factor.

sease. Since families have similar genes as well as similar environments, familial diseases could be due to shared genetic influences, to shared environmental factors, or to both. For some years, the role of one environment factor commonly shared by families, namely dietary salt (i.e., sodium chloride), has been studied at Brookhaven National Laboratory. These studies suggest that long excess salt intake 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 developed 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 long successive generations of those animals that failed to develop hypertension from salt intake, 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, sensitive strain (the "S" strain) has also been developed.

The availability of these two strains permits investigations possible. They provide a plausible laboratory model on which to investigate some clinical aspects of the human hypertension. More important, there might be the possibility of developing methods by which genetic susceptibility (敏感性) of human beings to high blood pressure can be defined without waiting for its appearance. Radioactive sodium 22 was an important "tool" in working out the characteristics of the sodium chloride metabolism.

The study of the effects of salt on high blood pressure was carried out_______.

A.as members of the same family tend to use similar amounts of salt

B.to explore the long-term use of a sodium based substance

C.because it was proven that salt caused high blood pressure

D.because of the availability of chemically pure salt and its derivatives

The main difference between "S" and "R" rats is their_______.A.need for sodium

B.rate of mating

C.type of blood

We can infer from the article that sodium 22 can be used to_______.A.control high blood pressure

B.cure high blood pressure caused by salt

C.tell the "S" rats from the "R" rats

D.determine what a sodium chloride metabolism is like

The most beneficial results of the research might be_______.A.development of diets free of salt

B.an early cure for high blood pressure

C.control of genetic agents that cause high blood pressure

D.the early identification of potential high blood pressure victims

Which of the statements best relates the main idea of this article？A.When salt is added rats and human beings react similarly.

B.The near future will see a cure for high blood pressure.

C.The medical field is desperately in need of research.

D.A tendency toward high blood pressure may be a hereditary factor.

请帮忙给出每个问题的正确答案和分析，谢谢！

Text 3

Under certain circumstances, the human body must cope with gases at greater-than-normal atmospheric pressure. For example, gas pressures increase rapidly during a dive made with scuba gear because the breathing equipment allows divers to stay underwater longer and dive deeper.

The pressure exerted on the human body increases by 1 atmosphere for every 10 meters of depth in seawater, so that at 30 meters in seawater a diver is exposed to a pressure of about 4 atmospheres. The pressure of the gases being breathed must equal the external pressure applied to the body, otherwise breathing is very difficult. Therefore all of the gases in the air breathed by a scuba diver at 40 meters are present at five times their usual pressure. Nitrogen, which composes 80 per cent of the air we breathe, usually causes a balmy feeling of well-being at this pressure. At a depth of 5 atmospheres, nitrogen causes symptoms resembling alcohol intoxication, known as nitrogen narcosis. Nitrogen narcosis apparently results from a direct effect on the brain of the large amounts of nitrogen cause under these pressurized helium does not exert a similar narcotic effect.

As a scuba diver descends, the pressure of nitrogen in the lungs increases. Nitrogen then diffuses from the lungs to the blood, and from the blood to body tissues. The reverse occurs when the diver surfaces; the nitrogen pressure in the lungs falls and the nitrogen diffuses from the tissues into the blood, and from the blood into the lungs. If the return to the surface is too rapid, nitrogen in the tissues and blood cannot diffuse out rapidly enough and nitrogen bubbles are formed. They can cause severe pains, particularly around the joints.

Another complication may result if the breath is held during ascent. During ascent from a depth of 10 meters, the volume of air in the lungs will double because the air pressure at the surface is only half of what it was at 10 meters. This change in volume may cause the lungs to distend and even rupture. This condition is called air embolism. To avoid this event, a diver must ascend slowly, never at a rate exceeding the rise of the exhaled air bubbles, and must exhale during as- cent.

31. What does the passage mainly discuss？

A) The equipment divers use.

B) The effects of pressure on gases in the human body.

C) How to prepare for a deep dive.

D) The symptoms of nitrogen bubbles in the bloodstream.

血压(blood pressure)

A.blood pressure

B.blood vessel

C.blood sugar

D.blood type

A．equal to the systolic blood pressure

B．equal to the diastolic blood pressure

C．the pressure of the fluid in the Bowman’s capsule

D．the difference in pressure between that of the blood in the glomerulus and the fluid in the first part of the nephron

A.stress

B.depression

C.flow

D.pressure