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Which of the following best expresses the author's main point of view？
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听力原文： In recent years many countries of the world have been faced with the problem of how to make their workers more productive. Some experts claim the answer is to make jobs more varied. But do more varied jobs lead to greater productivity？ There is evidence to suggest that while variety certainly makes the workers' life more enjoyable, it does not actually make him work harder. As far as increasing productivity is concerned, the variety is not an important factor.
Other experts feel that giving the worker freedom to do his job in his own way is important and there is no doubt that this is true. The problem is that this kind of freedom cannot easily be given in the modern factory with its complicated machinery which must be used in a fixed way. Thus while freedom of choice may be important, there is usually very little that can be done to create it. Another important consideration is how much each worker contributes to the product he is making. In most factories the worker sees only one small part of the product. Some car factories are now experimenting with having many small production lines rather than one large one, so that each worker contributes more to the production of the cars on his line. It would seem that not only is the degree of workers' contribution an important factor, therefore, but it is also one we can do something about.
To what extent does more money lead to greater productivity？ The workers themselves certainly think this is important. But perhaps they want more money only because the work they do is so boring. Money just lets them enjoy their spare time more. A similar argument may explain demands for shorter working hours. Perhaps ifwe succeed in making their jobs more interesting, they will neither want more money, nor will shorter working hours be so important to them.
(33)
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 flames up, the heat produced flows into the adjacent layer of unburned fuel and ignites it. In this way a zone of first spreads throughout the fuel mixture until the 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 openings 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. Another example is the hardening, and cracking of rubber with age. One way to avoid this is to incorporate certain chemicals called inhibitors into the compound.
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. This is the process that accounts for a major fire hazard, spontaneous combustion, as when oily rags suddenly burst 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.
c
A．Greater degree of one's contribution to work.B．Freedom to choose one's way of doing
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