Вопрос № 284263 - Английский язык

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The raw materials for plastics are coal and 1_______, and many plastic materials today are produced from oil. Plastics can be divided into two main 2_______. The first group, called thermoplastics, includes well-known plastics such as PVC, nylon and polythene. These can be treated (heated, softened and cooled) several times, and can be formed into combs, pipes and bags, in addition to many other similar 3_______.
Thermosetting 4_______ include melamine, polyurethane and phenolic resin, and can be made into tableware, foams and plugs respectively. However, this group differs from thermoplastics because they can be treated only once and harden when they are heated.

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Plastic Materials
1. Plastic materials are not found in nature. Plastic is formed by extrusion or injection molding under very high pressure. It can be molded into any desired shape. Organic plastics are divided into two general groups: thermosetting and thermoplastic. The thermosetting group becomes rigid through a chemical change that occurs when heat is applied. These plastics cannot be remolded. The thermoplastic group remains soft at high temperatures and must be cooled before becoming rigid. This group is not used generally as a structural material.
2. Plastics are rapidly becoming important construction materials because of their great variety, strength, durability and lightness. Plastics are light. The benefits of light weight coupled with good strength and absence of corrosion offer tremendous potential as alternatives to traditional building materials. A given volume of polythene weights less than one-eighth of an equal volume of iron and less than half of the same volume of aluminum.
3. Plastics are used in the industry and in the household: from rockets and electronics to toys and house ware. Plastic products offer many advantages over the materials they replace, such as ease of handling, lower maintenance costs and rapidity of assembly. The insulation and dielectric properties of plastics led to their early use in the electrical engineering industry, which was followed by special application in mechanical engineering.
4. Using of plastics as materials for a construction in the form of sheets, rods or tubes is substituting the conventional metals. Plastics offer a lot of properties for the designs. Plastics have now been developed to such an extent that they can be applied to almost every branch of building, from the laying of foundations to the final coat of paint.
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Why do plastics replace traditional building materials?

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Heat causes some 1_______ to expand more than others. For example, copper expands more than iron. This 2_______ is used in the bimetal strip, which consists of two dissimilar strips of metal welded together. The strips are usually made of brass (an alloy of copper and zinc) and invar, a ferrous alloy which expands very little when heated.
An increase in 3_______ causes the brass to expand more than the invar. This expansion causes the bimetal strip to bend, and consequently a switch or a valve is 4_______.

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The first scientists to study colour was Sir Isaac Newton. He was an English 1_______      who lived from 1642 to 1727. Newton was the first person to 2 _______ white light into different colours.
In 1861 another English scientist, James Clerk Maxwell, showed that he could make other colours by mixing the primary colours – red, blue and yellow – in different ways. These other colours are called secondary and tertiary colours. We make secondary colours by 3 _______ two primary colours together. For example, red and yellow become orange, yellow and blue become green, and blue and red become violet. We make tertiary colour with one 4_______ colour.
We can make a room look bigger or smaller, hotter or colder by using colour. Green and blue are cold colours. They can also make a room look bigger. Red, orange and yellow are hot colours. They can make a room look smaller.

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There have been many different number 1 _______ in the world. A long time ago the Babylonians counted in 60s and today computers count in 2s – using only 1 and 0. We call this 2-number system the binary system. Most systems, however, count in 10s. This is because we have 10 fingers. We call this system the decimal system from ‘decem’, the Latin word for 10.
The Romans used letters like I, V, X and C to 2 _______ in 10s but these are not very easy to use. The numbers most people use today come from India. We think they were 3 _______ by the Hindu people there. In the Hindu system the place of each number is important. For example, 832 is a different number to 238 or 382. The Hindu system was also used by the Arabs, and we now call them Arabic numbers. In about the 12th century an Italian called Leonardo Fibonacci wrote a book about Arabic numbers, and people all over Europe began using these numbers.
We do not know who invented the decimal point, but we know that in 1585 a man called Simon Stevin wrote  a book about the decimal point. The book was called ‘The Tenth’. Before we knew about the decimal point, we had to use 4 _______ like Ѕ and system ѕ when we talked about numbers smaller than 1.

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The Great Wall of China is so large that the men who landed on the moon could see it. It is the largest 1 _______ in the world.
It begins at Shanhaikun on the Yellow Sea and ends at Chaiyukan in the Gobi Desert. It is almost three thousand kilometers long. It is not only a wall, it has many thousands of 2 _______.
The Chinese people started building walls as early as 600 BC to keep out their enemies. However, it was the first emperor of China, Ch’in Shih Hwang-ti, who started the great Wall in about 214 BC. We get the word ‘China’ from his name.
Chinese workers built some of the Great Wall while Ch’in Shih Hwang-ti was emperor, bur most of it was 3 _______ much later, between 202 BC and 220 AD, and between 581 AD and 618 AD. After this time, no more work was done on the wall for hundreds of years, and much of it became broken. Then in the 15th century, the first of the Ming emperors started 4 _______ another wall near the first one. It is this wall that thousands of tourists visit every year.