Passage Three
For three groups of explorers formed by college students and young white collars,it started out as a wonderful trip. They were enjoying themselves exploring the Inner Mongolian desert. [32]But when the sandstorm came, the trip became a disaster.
The drama unfolded during the May Day holiday. One girl did not make it before the students were rescued. The group was eventually found with the help of a GPS receiver. GPS, or global positioning system, is a satellite-based navigation system made up of a network of 24 satellites. It was originally created for military use by the US in 1980s but is now available for civilian use. GPS works in any weather conditions, anywhere in the world, 24 hours a day. And the [34]service is free.
GPS satellites circle the earth twice a day and transmit signals and information to the earth. GPS receivers take this information and calculate the user's exact location. A GPS receiver must be locked on to the signals of at least three satellites to calculate the latitude and longitude of its location. With four or more satellites in view, the receiver can determine the user's altitude. [35]Once the user's position has been determined, the GPS receiver can calculate other information, such as speed, direction, distance to destination, and a whole lot more.

Questions 32 to 35 are based on the passage you have just heard.
32. What is true about the trip made by the young people?
正确答案：B
解析：录音开头提到：这三支探险队一开始的旅途非常愉快，但是，当沙尘暴袭来时，沙漠之旅变成了一场灾难。故B正确。
33. What is the main topic of the passage?
正确答案：C
解析：主旨题应该概括且含有核心词，符合此要求的是C，全篇大部分文字都是在介绍GPS及其功用。
34. Which of the following is true about the GPS?
正确答案：D
解析：考查对细节的记忆，符合短文听力“听到什么选什么”的解题原则，答案为D。A错在scientific research，应为military use；GPS在任何天气情况下都一样起作用，故B错；C中的指代有误，主语若是A GPS receiver才与原文相符，故也排除C。
35. What must be determined first before the GPS receiver can calculate other information?
正确答案：A
根据录音最后一句“一旦确定了使用者的位置，全球定位系统接收器就能计算其他的信息，如……”，可知A正确。