1999年5月托福考试听力全真试题

　　Today， we are going to take a look at the development of the skyscraper. We'll start with some buildings in Chicago. One of the circumstances that led Chicago to become home to some of the buildings now considered the prototypes for later skyscrapers was this： In 1871， there was a great fire that destroyed much of the city. It was that tragic fire that cleared the way for a new kind of city that used the new building techniques and new materials developed during the early 1800s.

　　One of these new structures was the Home Insurance Building， completed in 1885. It was ten storeys high. Now granted， that's no higher than some of the early skyscrapers in New York City. What made Chicago's Home Insurance Building important is that it had true skyscraper instruction with an internal metal skeleton that carried the weight of the brick exterior. This metal-support system along with the earlier development of the elevator were the two innovations that made the later very tall industrial buildings possible.

　　Chicago's Reliance Building was another important building in the development of the skyscraper. It showed the architects' understanding of the possibilities of mental frame construction by eliminating walls and opening up the sides as a glass box. It was the first expression of the skyscraper as the glass shelf framed in the metal grid.

　　40. Why does the professor mention the fire of 1871？

　　41. What was important about the Home Insurance Building？

　　42. What point does the professor make about the Reliance Building？

　　Questions 43-46 Listen to a lecture given in a mass communications class.

　　It was an Italian inventor who created the first wireless device for setting out radio signalsin 1895. But not until the American inventor Lee De Forest built the first amplifying vacuumtube in 1906 did we get the first radio as we know it. And the first actual radio broadcast wasmade on Christmas Eve of 1906. That's when someone working from an experimentalstation in Brand Rock， Massachusetts， arranged the program with two short musicalselections of poem and brief holiday greeting. The broadcast was heard by wirelessoperators on ships with a radio through several hundreds miles. The following year， DeForest began regular radio broadcasts in New York. These programs were similar to muchwhat we hear on radio today. In that， De Forest played only music. But because there werestill no home radio receivers， De Forest's audiences consisted only of wireless operators onships in New York Harbor. There is no doubt that radio broadcasting was quite a novelty inthose days， but it took a while to catch on commercially. Why？ Hmm， for the simple factthat only a few people， in fact， only those who tinkered with wireless telegraphs as a hobbyowned receivers. It wasn't until the 1920s that someone envisioned mass appeal for radio.This was radio pioneer David Sarnoff who predicted that one day there would be a radioreceiver in every home.

　　43. What is the talk mainly about？

　　44. Why were early radio broadcasts heard by such a small audience？

　　45. According to the talk， who owned the receivers in the early days of radio？

　　46. According to the talk， what did David Sarnoff predict about radios？

　　Questions 47-50 Listen to part of a talk in an astronomy class

　　The origin of Earth's moon， the largest moon in the solar system， is still something of amystery. There are some theories about its origin however. Now， keep in mind that a theoryof the moon's origin has to be consistent with two important facts. The first fact is that theEarth contains a lot of iron， most of it has an iron core. But the moon contains practically noiron. The second fact is that other than the difference in iron content， the moon and Earth arecomposed of accentually the same minerals， a similarity not shared with any other planet ormoon in our solar system.One of the earliest theories of the moon's origin， I called it the Capture Theory， proposes that the moon was somehow captured by Earth's gravitational force. This theory is improbable， however， because it assumes that the moon and Earth formed in different parts of the solar system. If this was true you would expect the moon's composition to be much different from Earth's composition， just as all the other planets in the solar system are so different from Earth.A second theory of the moon's origin is more promising. It is sometimes referred to as the Mars Theory， because according to this theory， when Earth was still molten， it was struck by a planet about the size of Mars. The impact caused the cores of the two planets to melt together and chunks of Earth's crust to be thrown out into space. These chunks came together to form the moon. Now， remember， Earth's crust is low in iron， because the iron is in Earth's core， but high in various other minerals. This then accounts for why there is little iron but lots of other minerals on the moon.

　　47. What is the talk mainly about？

　　48. According to the professor， what characteristic of Earth's moon should a theory of its origin be able to explain？

　　49. Why is the second theory sometimes referred to as the Mars Theory？

　　50. According to the Mars Theory， why does the moon contain little iron？