单选题The range in frequencies of musical sounds is approximately 20- 20,000 cycles per second (cy/sec), Some people can hear higher frequencies than others. Longitudinal waves whose frequencies are higher than those within the audible range are called ultrasonic frequencies. Ultrasonic frequencies are used in sonar for such purposes as submarine detection and depth finding. Ultrasonic frequencies are also being tried for sterilizing food since these frequencies kill some bacteria. Sound waves of all frequencies in the audible range travel at the same speed in the same medium. In the audible range, the higher the frequency of the sound the higher is the pitch. The term supersonic refers to speed greater than sound. An airplane traveling at supersonic speed is moving at a speed greater than the speed of sound in air at that temperature. Mach 1 means a speed equal to that of sound. Mach 2 means a speed equal to twice that of sound, etc. Musical sounds have three basic characteristics; pitch, loudness, and quality or timbre. As was indicated above, pitch is determined largely by the frequency of the wave reaching the ear. The higher the frequency the higher is the pitch. Loudness depends on the amplitude of the wave reaching the ear. For a given frequency, the greater the amplitude of the wave the louder the sound. To discuss quality of sound we need to clarify the concept of overtones. Sounds are produced by vibrating objects. If these objects are given a gentle push, they usually vibrate at one definite frequency producing a pure tone. This is the way a tuning fork is usually used. When objects vibrate freely after a force is momentarily applied, they are said to produce their natural frequency. Some objects, like strings and air columns, can vibrate naturally at more than one frequency at a time. The lowest frequency which an object can produce when vibrating freely is known as the object's fundamental frequency. Other frequencies that the object can produce are known as its overtones. The quality of a sound depends on the number and relative amplitude of the overtones present in the wave reaching the ear.

单选题You slip the key into the ignition and crank the engine to life. But before you put the ear into gear, you tap a key on the keyboard mounted by the steering wheel, and your newest e-mail flashes up on the windscreen. This seductive satyr is what you get when you cross a ear and a eomputer. Dubbed the "network vehiele", or net-mobile, it may soon come to a driveway near you ( probably the one belonging to your rich neighbor). In a net-mobile, a motorist could tap into a regional road system but also to map out a route around rush-hour traffic snags. Drivers and passengers will be able to send and receive e-mail, track the latest sports scores or stock quotes, surf the Web, and even play video games. Or so, at least, say a number of computer-industry firms such as Microsoft, Sun, IBM and Netseape. The modern car is already an electronic showcase on wheels . On-board microcomputers improve fuel economy and reduce emissions. They operate anti-lock brake systems, and on some ears even regulate the firmness of the shock absorbers. But much of the technology needed to add extra is available now. A prototype network vehicle, produced by a consortium of Netseape, Sun, IBM and Delco (an automotive electronics firm based in Michigan), was introduced at the recent annual computer industry show in Las Vegas. It not only offered such desktop-eomputer-like services as e-mail, but allowed a driver to use them without looking away from the road. It was operated by voice commands and projected its data on to the windscreen, using the same sort of head-up display system found in modern fighter jets. Members of the consortium think a real-world network vehicle could be in production in as little as four years. Car-makers have already begun rolling out some of the features found on these prototype net mobiles. If the driver of a General Motors car equipped with its On-Star system locks his key in the car, for example, an emergency centre can transmit a digital signal to unlock the doors. On-star also calls automatically for help if an accident triggers the airbags. Toyota and General Motors are among a growing list of firms offering such in-ear navigation systems. And in Europe, BMW and Mercedes-Benz recently introduced navigation hardware that can not only plot out a route, but alert a driver to traffic jams.

单选题In the end, a degree of sanity prevailed. The militant Hindus who had vowed to breach a police cordon and start the work of building a temple to the god Ram at the disputed site of Ayodhya decided to respect a Supreme Court decision barring them from the area. So charged have Hindu-Muslim relations in India become in recent weeks, as the declared deadline of March 15th neared, that a clash at Ram's supposed birthplace might well have provoked bloodshed on an appalling scale across the nation. It has, unfortunately, happened often enough before. But the threat has not vanished. The court's decision is only an interim one, and the main Hindu groups have not given up on their quest to build their temple. Extreme religious violence, which seemed in recent years to have faded after the Ayodhya-related explosion of 1992--1993, is again a feature of the political landscape. Though faults lie on both sides (it was a Muslim attack on Hindus in a train in Gujarat that started the recent slaughter), the great bulk of victims were, as always, Muslims. Once again, educated Hindus are.to be heard inveighing against the "appeasing" of Muslims through such concessions as separate constitutional status for Kashmir or the right to practice Islamic civil law. Once again, the police are being accused of doing little or nothing to help Muslim victims of rampaging Hindu mobs. Once again, India's 130m Muslims feel unequal and unsafe in their own country. Far too many Hindus would refuse to accept that it is “their own country" at all. The wonder of it, perhaps, is that things are not worse. While the world applauds Pakistan for at last locking up the leaders of its extreme religious groups, in India the zealots still support, sustain and to a degree constitute the government. The BJP, which leads the ruling coalition, was founded as a political front for the Hindu movement. It is simply one, and by no means the dominant, member of what is called the Sangh Pariwar, the "family of organizations". Other members of the family are much less savoury. There is the VHP, the World Hindu Organization, which led the movement to build the Ram temple. There is the Bajrang Dal, the brutalist "youth wing" of the VHP. There is substantial evidence that members of the VHP and the Bajrang Dal helped to organize the slaughter of hundreds of Muslims in Gujarat after 58 Hindus were killed on a train as they returned from Ayodhya.

单选题It would be a(n)______ thing to find a cat and a dog playing together.

单选题The Mayor asked the city council to recommend potential programs for the benefit of the Uindigent/U.

单选题 Making good coffee is not a simple business. Coffee bushes must be grown in shade. A hillside is best--but it mustn't be too {{U}}(1) {{/U}}. After three years, the bushes will start to {{U}}(2) {{/U}} bright-red coffee "cherries", which are picked, processed to {{U}}(3) {{/U}} the inner part, and spread out to dry for days, {{U}}(4) {{/U}} on concrete. They are {{U}}(5) {{/U}} again to separate the bean, which needs to rest, preferably for a few months. Only then can it be roasted, ground and brewed {{U}}(6) {{/U}} the stuff that dreams are suppressed with. In Mexico and parts of Central America, {{U}}(7) {{/U}} in Colombia, most coffee farmers are smallholders. They found it especially hard to {{U}}(8) {{/U}} the recent fall in the coffee price. The {{U}}(9) {{/U}} of their income makes it hard for farmers to invest to {{U}}(10) {{/U}} their crop, says Fernando Celis. The fall forced many small farmers to {{U}}(11) {{/U}} other crops, or migrate to cities. For farmers, one way out of this {{U}}(12) {{/U}} is to separate the price they are paid {{U}}(13) {{/U}} the international commodities markets. This is the {{U}}(14) {{/U}} of Fair-trade, an organization which certifies products as "responsibly" sourced. Fair-trade determines at what price farmers make what it considers a {{U}}(15) {{/U}} profit. Its current {{U}}(16) {{/U}} is that the appropriate figure is 10% above the market price. {{U}} (17) {{/U}}, sales of Fair-trade-certified coffee have increased from $ 22. 5m per year to $ 87m per year since 1998. This is still a tiny fraction of the overall world coffee trade, worth $10 billion {{U}}(18) {{/U}} But there are plenty of other markets for high-quality coffee. Some small producers can {{U}}(19) {{/U}} more by marketing their coffee as organic or "bird-friendly" because, unlike large, mechanized plantations, they have {{U}}(20) {{/U}} shade trees.

单选题For the people who have never traveled across the Atlantic the voyage is a fantasy. But for the people who cross it frequently one crossing of the Atlantic is very much like another, and they do not make the voyage for the (1) of its interest. Most of us are quite happy when we feel (2) to go to bed and pleased when the journey (3) On the first night this time I felt especially lazy and went to bed (4) earlier than usual. When I (5) my cabin, I was surprised (6) that I was to have a companion during my trip, which made me feel a little unhappy. I had expected (7) but there was a suitcase (8) mine in the opposite corner. I wondered who he could be and what he would be like. Soon afterwards he came in. He was the sort of man you might meet (9) ，except that he was wearing (10) good clothes that I made up my mind that we would not (11) whoever he was and did not say (12) .As I had expected, he did not talk to me either but went to bed immediately. I suppose I slept for several hours because when I woke up it was already the middle of the night. I felt cold but covered (13) as well as I could and tries to go back to sleep. Then I realized that a (14) was coming from the window opposite. I thought perhaps I had forgotten (15) the door, so I got up (16) the door but found it already locked from the inside. The cold air was coming from the window opposite. I crossed the room and (17) the moon shone through it on to the other bed. (18) there. It took me a minute or two to (19) the door myself. I realized that my companion (20) through the window into the sea.

单选题Cara Lang is 13. She lives in Boston, Massachusetts, in the US Last Thursday, she didn't go to school. She went to work with her father instead. Every year, on the fourth Thursday in April, millions of young girls go to work. This is Take Our Daughters to Work Day. The girls are between the ages of 9 and 15. They spend the day at work with an adult, usually a mother, father, aunt, or uncle. They go to offices, police stations, laboratories, and other places where their parents or other family members work. Next year, the day will include sons, too. The Ms. Foundation, an organization for women, started the program about ten years ago. In the US, many women work outside the home. The Ms. Foundation wanted girls to find out about many different kinds of jobs. Then, when the girls grow up, they can choose a job they like. Cara's father is a film director. Cara says," It was very exciting for me to go to the studio with my dad. I saw a lot of people doing different jobs. " Many businesses have special activities for girls on this day. Last year, Cara went to work with her aunt at the University of Massachusetts. In the engineering department, the girls learned to build a bridge with toothpicks and candy. In the chemistry department, they learned to use scales. They learned about many other kinds of jobs, too. Right now, Cara does not know what job she will have when she grows up. But because of Take Our Daughters to Work Day, she knows she has many choices.

单选题Today cognitive theorists empirically study the impact of feelings on cognitive processes such as memory and judgment and also the reciprocal influence of cognition on emotion. However, evolutionary theorists view emotion as a powerful source of motivation-an internal communication that something must be done. For example, when people are threatened, they feel fear, which in turn leads them to deal with the threatening situation through either fight or flight. Emotions and drives may also operate in tandem to motivate action, as when excitement accompanies sexual arousal. From an evolutionary perspective, different emotions serve different functions. Fear facilitates flight in the face of danger; disgust prevents ingestion of potentially toxic substances such as rotting meat. An emotion that is less well understood is jealousy. Why do people become jealous in intimate sexual relationships? One series of studies tested evolutionary hypotheses about differences in the concerns men and women have about their partners' fidelity. Since females can have only a limited number of children during their lifetimes, to maximize their reproductive success they should be motivated to form relationships with males who have resources and will contribute them to their offspring. Indeed, cross-cultural evidence demonstrates that one of the main mate selection criteria used by females around the world is mate resources. From a female's point of view, then, infidelity accompanied by emotional commitment to the other woman is a major threat to resources. A man unlikely to divert re- sources from his mate and her offspring to a casual fling, but the risk increases dramatically if he becomes emotionally involved and perhaps considers switching long-term partners. Hence, a woman's jealousy would be expected to focus on her mate's emotional commitment to another female. For males, the situation is different. If a male commits himself to an exclusive relationship with a female, he must be certain that the offspring in whom he is investing are his own. Since he cannot be sure of paternity, the best he can do is to prevent his mate from copulating with any other males. In males, then, jealousy would be expected to focus less on the female's emotional commitment or resources and more on her tendency to give other males sexual access. Indeed, in species ranging from insects to humans, males take extreme measures to prevent other males from inseminating their mates. In humans, male sexual jealousy is the leading cause of homicides and of spouse battering cross-culturally.

单选题This robot is supposed to save a lot of labor, but it remains a problem if it ______. A. is B. saves C. does D. has

单选题Evidence from. the economists and the building industries shows that______

单选题Euthanasia has been a topic of controversy in Europe since at least 1936. On an average of six times a day, a doctor in Holland practices "active" euthanasia: 1 administering a lethal drug to a 2 ill patient who has asked to be relieved 3 suffering. Twenty times a day, life prolonging treatment is withheld or withdrawn 4 there is no hope that it can 5 an ultimate cure. "Active" euthanasia remains a crime on the Dutch statute books, punishable 6 12 years in prison. But a series of court cases over the past 15 years has made it clear that a competent physician who 7 it out will not be prosecuted. Euthanasia, often called "mercy killing", is a crime everywhere in Western Europe. 8 more and more doctors and nurses in Britain, Germany, Holland and elsewhere readily 9 to practicing it, most often in the "passive" form of withholding or withdrawing 10 The long simmering euthanasia issue has lately 11 into a sometimes fierce public debate, 12 both sides claiming the mantle of ultimate righteousness. Those 13 to the practice see themselves 14 sacred principles of respect for life, 15 those in favor raise the banner of humane treatment. After years 16 the defensive, the advocates now seem to be 17 ground. Recent polls in Britain show that 72 percent of British 18 favor euthanasia in some circumstances. An astonishing 76 percent of 19 to a poll taken late last year in France said they would like the law changed to 20 mercy killings. Obviously, pressure groups favoring euthanasia and "assisted suicide" have grown steadily in Europe over the years.

单选题In the last paragraph, the author suggested that

单选题We should make a clear ______ between the two scientific terms for the purpose of our discussion. A. distinction B. discrimination C. deviation D. separation

单选题By the end of this month, all this ______.

单选题-- What are you going to do this afternoon? -- I'll probably go for a walk later on______it stays fine.

单选题From the newspaper, we can learn ______is going on in the world.