A pilot cannot fly a plane by sight alone. In many conditions, such as flyin

游客2025-02-02 36

问题 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 shouts 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 a short burst of radio waves: Then it receives the echoes produced when the waves bounce 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. [br] The word "shouts" underlined in Line 5 most probably means ______

选项 A、eavesdrops
B、yells
C、confesses
D、whispers

答案 B

解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。

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