单选题
A pilot cannot fly a plane by sight alone. In many conditions, such as flying at night and landing in dense fog, a pilot must use radar, an alternative way of navigating. Since human eyes are not very good at determining speeds of approaching objects, radar can show a pilot how fast nearby planes are moving. The basic principle of radar is exemplified by what happens when one {{U}}shouts{{/U}} in a cave. The echo of the sounds against the walls helps a person determine the size of the cave. With radar, however, the waves are radio waves instead of sound waves. Radio waves travel at the speed of light, about 300, 000 kilometers in one second. A radar set sends out {{U}}a short burst{{/U}} of radio waves: Then it receives the echoes produced when the waves {{U}}bounce{{/U}} off objects. By determining the time it takes for the echoes to return to the radar set, a trained technician can determine the distance between the radar set and other objects. The word "radar," in fact, gets its name from the term "radio detection and ranging." "Ranging" is the term for detection of the distance between an object and the radar set. Besides being of critical importance to pilots, radar is essential for air traffic control, tracking ships at sea, and for tracking weather systems and storms.
单选题 What is the main topic of this passage?
【正确答案】 A
【答案解析】[分析] 主旨题型 通读全文可见本文讲的是雷达的功用，工作原理，名字的来源等；因此选项A为答案。
单选题 According to the passage, what can a radar detect besides location of objects?
【正确答案】 C
【答案解析】[分析] 细节题型 见本文第三行：Since human eyes are not very good at determining speeds of approaching objects, radar can show a pilot how fast nearby planes are moving. (由于人眼并不擅长判定物体接近的速度，雷达就被用来给飞行员显示附近的飞机速度有多快)；因此可知雷达除了可探测物体的方位，还能探测物体的速度，选项C为答案。
单选题 The word "shouts" underlined in Line 5 most probably means ______
【正确答案】 B
【答案解析】[分析] 词义题型 见本文第五行：雷达的基本原理就像一个人在洞穴中 时所发生的事的例子一样。声音遇到墙壁(岩壁)后的回声可以帮助他判定洞穴的大小。既然shouts会有回声，且可助人判断洞穴的大小，应是“喊叫、呼叫”之类的意思，因此选项B为答案。
单选题 Which of the following words best describes the tone of this passage?
【正确答案】 C
【答案解析】[分析] 推断题型 通读全文可见本文使用举例的方式来讲解雷达的功用，工作原理，名字的来源等；因此可推断本文的语气是解释说明式的，选项C为答案。
单选题 The phrase "a burst" underlined in Paragraph 1 most probably means ______.
【正确答案】 B
【答案解析】[分析] 词义题型 见本文第8行：Radio waves travel at the speed of light, about 300, 000 kilometers in one second. A radar set sends out a short burst of radion waves. Then it receives the echoes produced when the waves bounce off objects. (无线电波以光的速度在传播，大约是每秒三十万公里；一个雷达装置发出______的无线电波，然后它接收无线电波遇到物体后反弹回来的回声/波)；在此“a short burst”of radion waves，应是指“一短束”无线电波，答案为B。
单选题 The word "it" underlined in Paragraph 1 refers to ______.
【正确答案】 A
【答案解析】[分析] 词义题型 参见第95题注释，可知“it”在此指前面所提到的“一个雷达装置”；因此A为答案。
单选题 Which of the following could best replace the word "bounce" underlined in Paragraph 1?
【正确答案】 D
【答案解析】[分析] 词义题型 参见第95题注释，Then it receives the echoes produced when the waves bounce off objects. (……然后它(一个雷达装置)接收无线电波遇到物体后______的回声/波)；既是回声/波，应是反弹回的；因此选项D“回弹”应为答案。
单选题 Which type of waves does radar use?
【正确答案】 C
【答案解析】[分析] 细节题型 根据文章介绍的雷达工作的基本原理，见文中第?行：With radar, however, the waves are radio waves instead of sound waves. (然而，雷达所使用的不是声波而是无线电波)；因此选项C为答案。
单选题 Which of the following would most likely be the topic of the next paragraph 1?
【正确答案】 B
【答案解析】[分析] 推断题型 通读全文可见本段开始介绍了飞行员在驾驶飞机时的局限，于是借助于雷达；接着介绍了雷达的工作原理，名字的来源，及其他功用等；由此判断有关介绍雷达的内容已告一段落，下一段应不会再讲雷达的其他功用(排除选项A)；本段因是围绕雷达来写，尽管提到雷达对飞行员起到举足轻重的作用，但目的不是向飞行员介绍不同种类的科学技术(排除选项C)；本段的目的也不是为了介绍飞行史(排除选项D)；因此只有选项B (使用声纳/声波定位仪这一技术)较为可能；声纳与雷达的工作原理近似，但更多用于水中；由此可假定本段讲了在空中和陆地上雷达的功用，下一段可能要讲解水中利用这一原理——声纳的应用；选项B为答案。
单选题 What might be inferred about radar?
【正确答案】 D
【答案解析】[分析] 推断题型 见本文第二句：In many conditions, such as flying at night and landing in dense fog, a pilot must use radar, an alternative way of navigating. (在许多情况下，如夜间飞行、在浓雾中降落；飞行员必须使用雷达——一种航行用的替代方法)；由此可推断雷达的使用除了使航行更为准确、弥补人类飞行员的不足之外，更重要的是它使得航行更为安全，因此选项D为答案。