Прочитайте текст и выполните задания. Rarefaction 1. Rarefaction is the reduction of an item’s densi...: ответ на тест 1088115 - Английский язык

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Rarefaction
1. Rarefaction is the reduction of an item’s density, the opposite of compression. Like compression, which can travel in waves (sound waves, for instance), rarefaction waves also exist in nature. A common rarefaction wave is the area of low relative pressure following a shock wave.
2. Rarefaction waves expand with time (much like sea waves spread out as they reach a beach); in most gases rarefaction waves keep the same «shape» at all times throughout the wave’s movement: it is a «self-similar expansion». Each part of the wave travels at the local speed of sound, in the local medium. This expansion behaviour is in contrast to the behaviour of pressure increases, which get narrower with time, until they steepen into shock waves.
3. A natural example of rarefaction occurs in the layers of Earth’s atmosphere. Because the atmosphere has mass, most atmospheric matter is nearer to the Earth due to the Earth’s gravitation. Therefore, air at higher layers of the atmosphere is less dense, or rarefied, relative to air at lower layers. Thus rarefaction can refer either to a reduction in density over space at a single point of time, or a reduction of density over time for one particular area.
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Rarefaction
1. Rarefaction is the reduction of an item’s density, the opposite of compression. Like compression, which can travel in waves (sound waves, for instance), rarefaction waves also exist in nature. A common rarefaction wave is the area of low relative pressure following a shock wave.
2. Rarefaction waves expand with time (much like sea waves spread out as they reach a beach); in most gases rarefaction waves keep the same «shape» at all times throughout the wave’s movement: it is a «self-similar expansion». Each part of the wave travels at the local speed of sound, in the local medium. This expansion behaviour is in contrast to the behaviour of pressure increases, which get narrower with time, until they steepen into shock waves.
3. A natural example of rarefaction occurs in the layers of Earth’s atmosphere. Because the atmosphere has mass, most atmospheric matter is nearer to the Earth due to the Earth’s gravitation. Therefore, air at higher layers of the atmosphere is less dense, or rarefied, relative to air at lower layers. Thus rarefaction can refer either to a reduction in density over space at a single point of time, or a reduction of density over time for one particular area.
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What layer of Earth’s atmosphere do rarefaction waves exist in?

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James Watt
1. James Watt was a Scottish inventor and mechanical engineer whose improvements to the Newcomen steam engine were fundamental to the changes brought by the Industrial Revolution in both his native Great Britain and the rest of the world.
2. While working as an instrument maker at the University of Glasgow, Watt became interested in the technology of steam engines. He realized that contemporary engine designs wasted a great deal of energy by repeatedly cooling and re-heating the cylinder. Watt introduced a design enhancement, the separate condenser, which avoided this waste of energy and radically improved the power, efficiency, and cost-effectiveness of steam engines. Eventually he adapted his engine to produce rotary motion, greatly broadening its use beyond pumping water.
3. Watt attempted to commercialize his invention, but experienced great financial difficulties until he entered a partnership with Matthew Boulton in 1775. The new firm of Boulton and Watt was eventually highly successful and Watt became a wealthy man. In his retirement, Watt continued to develop new inventions though none were as significant as his steam engine work.
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A rover
1. A rover is a space exploration vehicle designed to move across the surface of a planet or other celestial body. Some rovers have been designed to transport members of a human spaceflight crew; others have been partially or fully autonomous robots. Rovers usually arrive at the planetary surface on a lander-style spacecraft.
2. Rovers have several advantages over stationary landers: they examine more territory and they can be directed to interesting features. If they are solar powered, they can place themselves in sunny positions to weather winter months. They can also advance the knowledge of how to perform very remote robotic vehicle control which is necessarily semi-autonomous due to the finite speed of light.
3. Their advantages over orbiting spacecraft are that they can make observations to a microscopic level and can conduct physical experimentation. Disadvantages of rovers compared to orbiters are the higher chance of failure, due to landing and other risks.
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Twilight
1. Twilight is the illumination that is produced by sunlight scattering in the upper atmosphere, illuminating the lower atmosphere when the Sun itself is not directly visible because it is below the horizon, so that the surface of the Earth is neither completely lit nor completely dark.
2. The further the Sun is below the horizon, the dimmer the twilight (other things such as atmospheric conditions being equal). When the Sun reaches 18 degrees below the horizon, twilight’s brightness is nearly zero. Evening twilight ends and night begins. When the Sun again reaches 18 degrees below the horizon, night ends and morning twilight begins.
3. Twilight is defined according to the solar elevation angle, which is the position of the geometric center of the sun relative to the horizon. There are three established and widely accepted subcategories of twilight: civil twilight (brightest), nautical twilight («first light»), and astronomical twilight (darkest).
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Market Economies
1. In a true market economy the government plays no role in the management of the economy, the government does not intervene in it. The system is based on private enterprise with private ownership of the means of production and private supplies of capital, which can be defined as surplus income available for investment in new business activities. Workers are paid wages by employers according to how skilled they are and how many firms wish to employ them. They spend their wages on the products and services they need. Consumers are willing to spend more on products and services, which are favoured. Firms producing these goods will make more profits and this will persuade more firms to produce these particular goods rather than less favoured ones.
2. Thus, in a market economy consumers decide what is to be produced. Consumers will be willing to pay high prices for products they particularly desire. Firms, which are privately owned, see the opportunity of increased profits and produce the new fashionable and favoured products.
3. Such a system is, at first view, very attractive. The economy adjusts automatically to meet changing demands. No planners have to be employed, which allows more resources to be available for production. Firms tend to be highly competitive in such an environment. New advanced products and low prices are good ways to increase sales and profits. Since all firms are privately owned they try to make the largest profits possible.
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