Question

【題目】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 (戰(zhàn)略導(dǎo)彈)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】這是一篇說明文。文章介紹了雷達名稱的由來、歷史起源、作用原理以及在不同領(lǐng)域的應(yīng)用。

【1】根據(jù)前句Without radar, planes could not land safely in bad weather and ships could not move safely in thick fog.可知，沒有雷達，飛機不能在壞天氣中安全著陸，輪船不能在濃霧中安全航行，因此它對于航海和航空的人來說特別重要，故選D。

【2】根據(jù)前句But scientists did not make great advances in radar research until the 1930s, when the world was threatened by war.可知，科學(xué)家直到1930年代才在雷達技術(shù)上有了突破，再根據(jù)后句It has been used widely in almost every conflict since then.（自此之后被廣泛用于各種沖突斗爭中），故E項“在二戰(zhàn)中雷達開始被有效地使用”符合上下文文意，故選E。

【3】根據(jù)前句On the screen an observer sees a flash, or a blip, that shows the direction and distance of the object.可知，在屏幕上觀察者看到了一束光，這表明了物體的方向和距離。下面應(yīng)該是對這些測量的評價，說明這些測量是高度準(zhǔn)確的。故選B。

【4】此段主要介紹了radar在不同領(lǐng)域的應(yīng)用。前面列舉機場控制塔，防止輪船撞冰山或其他船，后面列舉天氣預(yù)報，天文學(xué)家等，所以此處也是列舉，故選A。

【5】根據(jù)后文內(nèi)容可知，雷達天線被安裝用于保衛(wèi)國土，由此可知加強國家防衛(wèi)也是雷達的重要功能之一。故選G。