Прочитайте текст Concrete is produced by combining coarse and fine aggregates Portland cement and wa...: ответ на тест 800547 - Английский язык

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Concrete is produced by combining coarse and fine aggregates, Portland cement, and water. Coarse aggregate is generally gravel or crushed stone, and fine aggregate is sand. Cement, sand, gravel and water are taken in proportional amounts and mixed. The quality of concrete depends mostly on the quality of the cement used. The process of production consists in pouring the mixed components into forms and holding them there until they harden. The process of hardening generally lasts for about 28 days.
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What does the quality of concrete depend on?

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Concrete is produced by combining coarse and fine aggregates, Portland cement, and water. Coarse aggregate is generally gravel or crushed stone, and fine aggregate is sand. Cement, sand, gravel and water are taken in proportional amounts and mixed. The quality of concrete depends mostly on the quality of the cement used. The process of production consists in pouring the mixed components into forms and holding them there until they harden. The process of hardening generally lasts for about 28 days.
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What does the quality of concrete depend on?

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What is a crystal? A crystal is a geometrical solid made by a natural process. Many substances absorb water from solutions when they crystallize; that is, they unite chemically with a definite proportion of water. The water with which any substance unites during the process of crystallization is called the water of crystallization.
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What is a crystal?

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Aluminium, water, oxygen, and carbon dioxide are substances. Some substances are elements and some substances are compounds. Elements have only one type of atom whereas compounds have more than one type.
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How many types of atom do elements have?

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Engineering is putting knowledge of Nature to practical use. The end result of engineering is some physical thing: a machine, a tool, a gadget. Engineering is solving problems. It’s convenient to discuss engineering projects within the framework of five steps for solving problems: define the problem, identify possible solutions, select a solution, implement the solution, verify the solution.
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What is the end result of engineering?

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Mrs. Sara Winchester of San Jose, California, was a very strange woman who built one of the world’s most unusual houses. When she died in 1922, aged 85, she was living alone in a house that had more than 150 rooms and covered an area of land greater than 2.5 hectares.
Mrs. Winchester’s problem was that she believed that if she stopped adding rooms to her house, she would die. Therefore, she employed workmen to keep on building and was happy only when she heard the sound of building. The house, when she bought it in 1884, was quite small, but 38 years later it was huge.
When she bought it, the house had two floors. By the time she died, it had eight. It had three lifts, 48 fireplaces and nine kitchens – none of which was ever used. In total, there were 2,000 doors and 10,000 windows. There were also miles of secret passages and tunnels that no one, not even Mrs. Winchester, knew how to get in to or out of.
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What was Mrs. Winchester’s problem?