Post-text exercises: 1. Put the words in the right order to make a sentence:

1. Or, of, in, off, the, any, dish, microwaves, their, radar, pulses, radio, antenna, waves, object, or, which, path, transmits, bounce. 2. Fog, sleet, are, to, such, clouds, and, visible, transparent, waves, as, rain, snow, that, such, falling, block, things, light, usually, radio. 3. In, are, not, the, as, the, receivers, always, same, radar, usually, location, but, transmitter. 4. Has, directions, signals, a, called, radar, in, radio, that, system, emits, transmitter, waves, radar, predetermined. 5. Radar, Britain, in, during, and, practical, II, nations, was, World, other, War, developed, secrecy, by. 6. Has, English, radar, noun, all, the, since, languages, losing, term, entered, and, the, capitalization, common, other, as, radar. 7. Reflected, desirable, are, make, the, towards, radar, as, radar, back, transmitter, that, work, signals, the, ones, make. 8. With, into, they, are, or, in, when, contact, usually, scattered, directions, these, an, reflected, many, come, object, and.
И вот текст под это задание:
Radar is an object-detection system which uses electromagnetic waves—specifically radio waves—to determine the range, altitude, direction, or speed of both moving and fixed objects such as aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish, or antenna, transmits pulses of radio waves or microwaves which bounce off any object in their path. The object returns a tiny part of the wave's energy to a dish or antenna which is usually located at the same site as the transmitter.

Practical radar was developed in secrecy during World War II by Britain and other nations. The term RADAR was coined in 1940 by the U.S. Navy as an acronym for radio detection and ranging. The term radar has since entered the English and other languages as the common noun radar, losing all capitalization. In the United Kingdom, the technology was initially called RDF (range and direction finding), using the same initials used for radio direction finding to conceal its ranging capability.

A radar system has a transmitter that emits radio waves called radar signals in predetermined directions. When these come into contact with an object they are usually reflected and/or scattered in many directions. Radar signals are reflected especially well by materials of considerable electrical conductivity—especially by most metals, by seawater, by wet land, and by wetlands. Some of these make the use of radar altimeters possible. The radar signals that are reflected back towards the transmitter are the desirable ones that make radar work. If the object is moving either closer or farther away, there is a slight change in the frequency of the radio waves, due to the Doppler effect.

Radar receivers are usually, but not always, in the same location as the transmitter. Although the reflected radar signals captured by the receiving antenna are usually very weak, these signals can be strengthened by the electronic amplifiers that all radar sets contain. The weak absorption of radio waves by the medium through which it passes is what enables radar sets to detect objects at relatively-long ranges—ranges at which other electromagnetic wavelengths, such as visible light, infrared light, and ultraviolet light, are too strongly attenuated. In particular, there are weather conditions under which radar works well regardless of the weather. Such things as fog, clouds, rain, falling snow, and sleet that block visible light are usually transparent to radio waves. Certain, specific radio frequencies that are absorbed or scattered by water vapor, raindrops, or atmospheric gases are avoided in designing radars except when detection of these is intended.