10 Use the Past Simple, Present Perfect, Past Perfect of the verbs in the brackets and translate the sentences:

1. Since 1897 much ( to be learned) about the structure of atom. 2. After Becquerel ( to make )a great number of experiments, he discovered the phenomenon of radioactivity. 3. In 1898 the Curies ( to discover) a new substance which they ( to receive) during their experiments. They found that it ( to be ) much more active. 4. By the end of 1898 the Curies ( to obtain) the element radium. They announced that they ( to discover ) it in December 1898. 5. In 1969 people ( to mark ) the 100^th anniversary of the discovery by Mendeleev of the periodic law of chemical elements. 6. After we ( to construct) a number of new power stations, our country will get cheap electric power. 7. In 1761 M. V. Lomonosov, with the aid of a telescope, ( to discover) a luminous rim around Venus. He explained that this phenomenon ( to be caused ) by the existence of an atmosphere around Venus.8. Observations showed that the luminous rim ( to be ) really the planet’s atmosphere lit up by the sun. It ( to be observed) in 1882, and will not be seen again until 2004. 9. Man ( to achieve ) great successes in the fieldof studying the structure of new elementary particles.

11. Translate the following sentences into English using the corresponding Tenses:

1. Він був щасливий: він написав чудовий твір.2.Я шукаю тебе весь вечір. 3. Я раптом згадав, що нічого не їв з ранку. 4. На щастя, дощ уже перестав, коли ми вийшли. 5. Скільки років ви працюєте в цій школі? 6. Об одинадцятій годині ми вже працювали протягом трьох годин. 8. Я вже тричі говорив тобі, що треба переписати вправу. 9. Я вже цілу годину читав після обіду, коли прийшов тато. 10. Я не прийду. Я писатиму твір увесь вечір. 11. Де ти був з минулої п’ятниці? 12. Я вже два тижні живу у друзів. 13. Я вже два тижні жив у друзів, коли одержав листа. 14. Скільки днів ви вже читаєте цю книжку? 15. Лише коли вона була у поїзді, вона згадала, що залишила книжку вдома. 16. Вони живуть у цьому будинку вже п’ять років. 17. Моя сестра була хвора вже кілька днів, коли я дізнався про це. 18. Ти знав, що він не написав твір? 19. Ми не одержуємо від неї листів уже кілька місяців. 20. Скільки років ви вже працюєте на цьому заводі? 21. Він уже пішов, коли Олена ввімкнула радіо. 22. Я працюю над цією проблемою вже три місяці. 23. Ви повинні відпочити. Ви занадто багато працювали сьогодні.

LESSON 83

CITY GARBAGE: PROBLEMS AND SOLUTIONS

PART I

Almost everything that is produced for human needs, with time becomes garbage. All sorts of methods have been tried to get rid of refuse. It has been buried, removed as far as possible from population centres. Nevertheless, even in antiquity Rome lost the “battle”: garbage filled its famous Forum.

In our time the problem of domestic waste disposal has acquired a global nature. Cities with populations of several million form Everests of garbage. Every urbanite throws away nearly a tonne of unwanted things annually. They wind up in the city garbage dumps, which take up hundreds of hectares of land, putting it out of useful circulation. Moreover, all such dumps are unanitary. The mountains of garbage attract incalculablehordes of rodents and birds, which spread decomposition products. Rain water becomes saturated with noxious substances which subsequently penetrate into underground water and poison them. Not only does grass not grow on the sites of former dumps, but construction work and the laying of supply lines in these areas have to be banned for 50 to 100 years.

Many useful elements, including those of organic origin, are irretrievably lost in garbage dumps. While taking them from nature and in enormous quantities, man gives nothing back to it. On the contrary, he keeps on taking in order to turn out new consumer goods. Eventually, this can seriously upset the ecological balance.

The most effective method of waste disposal is to utilize it, in other words, to process it industrially.

HOW IS THIS DONE?

Different countries handle this engineering problem in different ways. Experts have developed many production processess which make it possible to reconvert mountains of garbage into substances that are of crucial importance to industry and agriculture. Among such enterprises is the St. Peterburg automatic plant which processess solid domestic waste. It alone “gobbles up” 35-40 per cent of the city’s tips – 900,000 cubic metres.

The garbage is first fed to belt conveyers, where magnetic separators extract ferrous metals from it, which are subsequently pressed into compact briquettes and shipped to metallurgical plants for resmelting. Domestic wastes, in particular tin cans ( and other discarded objects as well), also contain valuable materials like tin, copper, zinc and brass. Until recently they were extracted in the metallurgical plants which receive the briquettes, but now this is being done in the automatic plant itself – in special newly built departments.

Refuse relieved of metal then goes into biothermal drums – enormous cylinders up to 60 metres long and four metres in diameter. They slowly rotate, mixing the waste. The air which is fed into the drums provokes an intensive aerobic process. Under the action of microorganisms all the garbage’s organic components decompose. The temperature of what is no longer waste, but is known as the compost mass, rises to 60 – 70 C. As a result, the disease-producing microbes die and the substance in the drums becomes harmless.

In 48 hours the compost mass ripens. Nevertheless, it still contains a wide variety of particles and fragments which biothermal treatment leaves unchanged. In order to dispose them the mass is sifted through giant sieves, where the material processed in the biothermal drums is separated into compost and ballast. Now the main thing is to get rid of glass fragments – enemy number one of compost. Obviously, fertilizer containing glass fragments cannot be introduced into soil.However, if they are reduced to the size of grains of sand and rolled smooth, they can no longer harm the roots of future plants.

To this end, all the material sifted through the giant sieves goes into a vertical shaft in which it gets into an upward air current. The light particles – mostly organic – are carried off. The particles of glass and ceramics which are left go to thegrinding zone.

The ballast which fails to pass through the sieve - rubber, plastics and wood fragments had to be taken back to the garbage dumps, and this type of refuse accounts for almost a quarter of all domestic waste. Now even this ballast is processed – by pyrolisis, or the thermal disintegration of complex substances into simpler ones. As a result valuable products are obtained, such as fuel gas, bituminous resins and solid carbonaceous compounds, which in our day find broad application as graphite substitute in metallurgy.

The plant’s final and main product is compost. It looks like ordinary earth. In fact, it is a biologically active substance which can be used far more effectively than an ordinary fertilizer. Due to a high temperature it is possible to employ it as a biological fuel to heat the soil in hot-houses. The compost’s biological energy is sufficient to grow two crops. After that, it can be transformed to open ground as an ordinary fertilizer.

The Leningrad plant was the Soviet Union’s first enterprise which almost wholly restores to the nationaleconomy what is contained in city dumps. Not only does it pollute the environment in any way, it does not even consume water on its technological requirements.