题目内容
Rocket fuels are more explosive than methane gas because of ______.
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Part A
Directions: Read the following four texts. Answer the questions below each text by choosing A, B, C or D. (40 points)
A classic series of experiments to determine the effects of overpopulation on communities of rats was conducted by a psychologist, John Calhoun. In each experiment, an equal number of male and female adult rats were placed in an enclosure. The rat populations were allowed to increase. Calhoun knew from experience approximately how many rats could live in the enclosures without experiencing stress due to over crowding. He allowed the population to increase to approximately twice this number. Then he stabilized the population by removing offspring that were not dependent on their mothers. At the end of the experiments, Calhoun was able to conclude that overcrowding causes a break down in the normal social relationships among rats, a kind of social disease. The rats in the experiments did not follow the same patterns of behavior. as rats would in a community without overcrowding.
The females in the rat population were the most seriously affected by the high population density. For example, mothers sometimes abandoned their pups, and, without their mothers' care, the pups died. The experiments verified that in overpopulated communities, mother rats do not-behave normally. Their behavior. may be considered diseased, pathological. The dominant males in the rat population were the least affected by overpopulation. Each of these strong males claimed an area of the enclosure as his own. Therefore, these individuals did not experience the overcrowding in the same way as the other rats did. However, dominant males did behave pathologically at times. Their antisocial behavior. consisted of attacks on weaker male, female, and immature rats. This deviant behaviour showed that even though the dominant males had enough living space, they too were affected by the general overcrowding.
Nondominant males in the experimental rat communities also exhibited deviant social behavior. Some withdrew completely, avoiding contact with other rats. Other nondominant males were hyperactive, chasing other rats and fighting each other.
The behaviour of the rat population has parallels in human behavior. People in densely populated areas exhibit deviant behavior. similar to that of the rats in Calhoun's experiments. In large urban areas, such as New York City, London, and Cairo, there are abandoned children. There are cruel, powerful individuals, both men and women. There are also people who withdraw and people who become hyperactive. Is the principal cause of these disorders overpopulation？ Calhoun's experiments suggest that it might be. In any case, social scientists and city planners have been influenced by the results of this series of experiments.
Calhoun stabilized the rat population ______.
国内生产总值(GDP)是指在一国的领土范围内，本国居民在一定时期内所产生的、以市场价格表示的产品和劳务总值。 ()
A typical combustion process is the burning of gasoline in an automobile engine. The vaporized fuel is mixed with air, compressed in the engine's cylinder, and ignited by a spark. As the fuel flame up, the heat produced flows into the adjacent layer of unburned fuel and ignites it. In this way a zone of fire spreads throughout the fuel mixture is called a combustion wave.
The speed at which such a combustion wave travels through a fuel mixture is called the burning velocity of the mixture. The burning velocity of a gas such as methane quietly burning in air is only about one foot per second. By comparison, the burning velocity of more reactive combinations such as the rocket Fuels, hydrogen and fluorine, can be hundreds of feet per second.
If the fuel flows at the same speed as the combustion wave, the result is a stationary flame, like the one in your kitchen gas burner. In the kitchen burner a jet of gas mixed with airflows from the opening in the head of the burner. If the velocity of the fuel mixture flowing from the opening is greater than its burning velocity, the flame blows out.
In jet engines speeding through the air at 500 to 600 miles per hour, the engine's flame is sometimes blown out by the blast of air entering the combustion chamber at high speeds. Jet pilots call this condition "flameout".
Combustion can sometimes occur very slowly. A familiar example of slow combustion is the drying of ordinary oil-based paint. In this chemical reaction, called oxidation, the oxygen in the air reacts with the drying oil in the paint to provide a tough film. The linseed oil molecules link together, forming an insoluble coating.
How can the chemical reaction involved in such a quiet process as the drying of paint also produce spectacular flames and explosions？ The main difference between the two is the temperature at which they occur.
At lower temperatures the reaction must take place over a long time. The heat which is slowly produced is dissipated to the surroundings and does not speed up the reaction. When the heat produced by the low-temperature reaction is retained instead of being dissipated, the system breaks into flame.
In a flame or explosion, the reactions are extremely fast. In many chemical processes, however, such a rapid oxidation process would be extremely destructive.
Which of the following states the major difference between oxidation and fire？
同样是10000元存款，分别存为三个月期(自动转存)和一年期的整存整取定期存款，由于三个月期限的存款每到三个月时，利息可以计入本金重新作为计息起点，所以一年过后，两种存款方式中，一年期整存整取获得的利息金额一定较低。 ()
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