1.Tom had returned from the cinema by five o’clock.
2.Last night we went to a football match.
3.What did you do yesterday ?
4.When Nick rang me up yesterday,I was helping mother.
5.What will your brother do tomorrow ?
6.His sister studies English every day.
7.What is mother doing now ?
8.What were you doing at four o’ clock yesterday?
9.She has just gone out.
10.When I came , mother has already cooked dinner.
11.I have never been to Greece.
12. Look ! What beautiful flowers she has just bought!
13. Let’s go for a walk.The rain has stopped and the sun is shining.
14. She has already been doing her homework for two hours, but she hasn't done yet a half of it.
15.This man is a writer.
16.At last I translated this article: now I ‘ll have a little rest.
17.Did you play the piano yesterday ?
18. He was driving around the town for half an hour.
19. My parents haven't paied for tickets yet.
20. Sam often wakes up at half past six in the morning.
At the present time the significant changes have been occuring and they are not always positive. Ozone layer protects the earth’s surface from the sun's ultraviolet rays, debilitating the organism's ability to withstand the diseases. It is broken by chlorofluorocarbon, utilizing in aerosol production, in the manufacture of materials for the sterilization of medical equipment and etc. The greenhouse effect and acid rains are the result of burning of the fossil fuels, disposable by different sources. Mass cutting down of forests leads to disruption of the process of rotation the oxygen and carbon in the biosphere. Ecological balance is disrupted also by plenty of disposable garbage and water pollution by harmful substances.
Every year a lot of species of plants and animals have been destroying , forest cover has been exterminating, mineral reserves have been decreasing, the world ocean has been becoming depleted. These losses are incommensurable.
The global environmental crisis may turn into a catastrophe for the planet in the future. If mankind doesn’t change the way of consumption the natural resources, there will begin famine, deficit of clean water and outburst natural disasters. The environmental crisis is overcame by means of ecological education of all stratum of the society, creation of effective nature conservation legislation, implementation the good scientific and technical solutions, applying the conservation ecology.