Question

【题目】Radar is an electronic device that detects planes, ships, coastlines, landmarks, and even storm clouds. The name radar comes from the first letters of the words radio direction and ranging. As the human eye uses light waves to see, radar “sees” with radio waves. Without radar, planes could not land safely in bad weather and ships could not move safely in thick fog. 【1】

In the 1800s it was discovered that radio waves could be reflected from objects. But scientists did not make great advances in radar research until the 1930s, when the world was threatened by war.【2】 It has been used widely in almost every conflict since then.

Echoes make it possible for radar to work. When a beam of radio waves is sent out, it strikes on an object and returns an echo. This echo is picked up by radar and recorded on a screen similar to television screen. On the screen an observer sees a flash, or a blip, that shows the direction and distance of the object. 【3】

Airport control towers use radar to guide planes in for safe landings. Almost all large ships depend on radar to prevent collisions with icebergs or other ships.【4】Weather forecasters “see” the size, direction, and speed of storms on radar screens. Astronomers can even use radar to measure accurately the distance to the moon. Thus, the device has generated major advancements.

【5】Huge radar antennas have been installed all over the United States. They guard us against possible enemy attacks. We have ballistic—missiles (战略导弹)warning systems that can alert us to attacks when missiles are more than 1,000 miles away. Other radar systems warn us against enemy aircraft and even spying space satellites.

A. Police track speeders in radar-equipped cars.

B. These measurements are now highly accurate.

C. The device can be used in a wide range of fields.

D. It is therefore especially valuable to shippers and travelers.

E. During World War II many countries used radar effectively.

F. Today radar is used by commercial airliners and weather forecasters.

G. Strengthening national defense is one of radar’s most important functions.

Answer 1

【答案】

【1】D

【2】E

【3】B

【4】A

【5】G

【解析】这是一篇说明文。文章介绍了雷达名称的由来、历史起源、作用原理以及在不同领域的应用。

【1】根据前句Without radar, planes could not land safely in bad weather and ships could not move safely in thick fog.可知，没有雷达，飞机不能在坏天气中安全着陆，轮船不能在浓雾中安全航行，因此它对于航海和航空的人来说特别重要，故选D。

【2】根据前句But scientists did not make great advances in radar research until the 1930s, when the world was threatened by war.可知，科学家直到1930年代才在雷达技术上有了突破，再根据后句It has been used widely in almost every conflict since then.（自此之后被广泛用于各种冲突斗争中），故E项“在二战中雷达开始被有效地使用”符合上下文文意，故选E。

【3】根据前句On the screen an observer sees a flash, or a blip, that shows the direction and distance of the object.可知，在屏幕上观察者看到了一束光，这表明了物体的方向和距离。下面应该是对这些测量的评价，说明这些测量是高度准确的。故选B。

【4】此段主要介绍了radar在不同领域的应用。前面列举机场控制塔，防止轮船撞冰山或其他船，后面列举天气预报，天文学家等，所以此处也是列举，故选A。

【5】根据后文内容可知，雷达天线被安装用于保卫国土，由此可知加强国家防卫也是雷达的重要功能之一。故选G。