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ngan271102@gmail.com said:

[A] Getting from place to place has been a challenge for humans since the beginning of man’s existence. Not only do people struggle with the actually physical problems of travel, but they also need to know the right direction to go. In one’s own little part of the world, this may have been relatively easy, but, as humans expanded further and further, it became necessary to determine how to get from one place to another and back again. Paths, roads, and trails made journeys easier, and the creation of maps transmitted this knowledge to others.

However, once humans pushed onto the vast oceans, there were no roads or accurate maps. The compass, showing the magnetic north, was a great, yet imperfect, aid. Latitude could be measured by sun angles, but until the perfection of timepieces in the 19th century, it was almost impossible to measure longitude. Fortunately, today there is a device which allows people easily to find their position no matter where they are: the Global Positioning System (GPS).
[C] The Global Positioning System consists of a series of twenty-four satellites in geosynchronous orbit around Earth at an altitude of 12,500 miles. These satellites are in fixed positions, so, by reading the signal from three of them, a person holding a GPS receiver can know exactly where he is. The GPS receiver synchronizes its clock with that of the satellites’ atomic clocks. The receiver then measures how long it takes a signal from one satellite to reach it and calculates the distance from the satellite. At the same time, it is calculating the distance from two other satellites in a process called triangulation. Once these calculations take place, the receiver knows exactly where a person is and shows the coordinates. On more modern devices used in vehicles, it even shows an animated car exactly where it is on a city grid.

[D]This miraculous system is the legacy of the United States military. When the Russians launched the world’s first satellite, Sputnik, in 1957, many scientists immediately grasped that satellites could be used for navigation purposes. By 1964, four American satellites were being used to help US naval vessels navigate. Called Transit, the system took up to ninety minutes to give a position report, which was too slow for ever-changing battlefield situations. With the advent of the Vietnam War, the Air Force and Army wanted a system to help them navigate over the jungles of Southeast Asia. Unfortunately, the Navy, Air Force, and Army competed with each other to build different systems, wasting resources and time on creating three systems instead of one.

[E] This all changed in 1973. The Department of Defense ordered Air Force Colonel Brad Parkinson to head a team to create a navigation system that all three branches of the military and civilians could use. If anyone can be called the father of GPS, Parkinson deserves the title. Putting aside service rivalries, Parkinson’s team created a plan that implemented the aspects of all three services’ navigation systems. By 1978, the system was ready and being tested, with the eventual cost of the system being four billion dollars. After the successful implementation of the GPS system, Parkinson retired from the Air Force, eventually becoming a professor at Stanford University. The military, afraid that rival countries and civilians would use the system to attack America or for criminal purposes, installed a distortion in the GPS receivers. Military units had a way to eliminate the error. In 2000, the US President told the military to eliminate the distortion.

[F]The applications of GPS are wide-ranging. Police, fire, and other emergency services around the world have made it part of their normal operating equipment. It is even used to keep track of criminals on day leave or parole. By the turn of the century, GPS receiving devices became more inexpensive and are now affordable for much of the public. They are becoming standard in most new car designs and are a favorite of hunters and fishermen making long treks in the wilderness. Some day in the future, people may be able to fit their children with miniature tracking devices so that they can use GPS to know where they are at all times. While many anxious parents may welcome this, others are already beginning to wonder if the GPS revolution is just another way for the government to infringe on its citizens’ privacy.

Question 1.The word ‘transmitted’ in paragraph A is closest in meaning to .
A. passed on
B. sent out
C. took in
D. moved on

Question 2.It can be inferred from paragraph C that
A. none of the twenty-four satellites has ever failed to function.
B. a GPS receiver will always be in range of at least three satellites.
C. GPS receivers have atomic clocks to keep track of time.
D. all GPS receivers use animation that makes them user-friendly.

Question 3.According to paragraph D which of the following is true of Global Positioning System?
A. Work on it began as soon as the Soviets launched Sputnik.
B. It was developed out of necessity during the Vietnam War.
C. Its basis was the system used by the US Navy called Transit.
D. It was created during a joint operation of the US military.

Question 4.According the passage, the biggest obstacle to creating GPS was .
A. inter-service rivalries that existed in the American military
B. not enough money being spent on research and development
C. technological problems that prohibited building an accurate system
D. a lack of support from the government in eliminating problems

Question 5.According to paragraph E, the American military distorted the GPS signal because .
A. they refused to give away the secret of GPS to other countries
B. they were concerned that the device would be used against them
C. they wanted to prevent criminals from accessing the system
D. it was classified technology that foreign nationals should not have

Question 6.Why does the author mention the cost of GPS receiving devices in paragraph F?
A. to explain why they are now becoming more popular than in the past.
B. to show that scientists have found ways to make them less expensive.
C. to highlight that many companies produce them, thereby driving prices down.
D. to prove that even the poorest person can afford to purchase one.

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