use the past indefinite or the past perfect in adverbial clauses of time.

1.when mr.scott (saw/had seen) he visitor, he got very angry.
2.as soon as the orchestra (began/had begun) to play, john left the hall.
3.when she (tidied up/had tidied up) the bedrooms, she went downstairs to have a rest.
4.when the students (took/had taken) their seats, the professor began his lecture.
5.when they were leaving the restaurant, it began to rain havily and they (had/had had) to go back.
6.when dikran (made/had made) his speech, everybody began to applaud.
7.he called me as soon as he (got/had got) home.
8.when they (knew/had known) me for a year, they invited me to dinner.
9.he refused to leave until he (saw/had seen) the manager.
10.he (was/had been) in the army for a year when his father died.

1.  The Earth's weather is regulated by rainforests.

2.  Only 2 percent of 250,000 known plant species have been investigated (by scientists) for their possible medicinal value.

3.  Projects to ensure the survival of the ecosystem are constantly being developed by environmentalists.

4.  Tougher environmental laws will need to be passed by governments and elected officials.

5.  The Hawaiian monk seal was nearly driven to extinction by the oil exploration business.

6.  The environment was being protected by Greenpeace long before it became fashionable.

7.  The blue whale had been hunted by whalers almost to extinction.

8. According to some estimates, greenhouse emissions will have been reduced by countries in five years.

9.  A predator had never been faced by the dodo before its natural habitat was invaded by humans.

10. The elephant population is going to be destroyed by illegal hunters.

Olympic Games Lots of people in the world are fond of sport, because it’s not only healthy, but also spectacular and exciting. For these reason people have started the Olympic Games. They have appeared in 776 BC in Ancient Greece, where people every four years held festivals to please the ancient God Zeus. Later on the Games have disappeared and were revived in the present era, in 1896. The first modern Olympics took place in the capital of Greece, Athens. The old tradition to hold the Games every four years was also revived. So, from then on the Olympic Games took place every four years in different cities of the world. At certain times, such as Second World War, the games were forbidden. The Olympic Games are considered to be the biggest international sports games, which unite people from all over the world. There are two types of Olympic Games: Summer Olympics and Winter Olympics. Ancient Greeks didn’t have Winter Games, so the first Winter Olympics were held in 1924 in France. The official emblem of the Olympic Games is a colourful flag with five interlinked rings. The colours of the rings are blue, red, yellow, green and black, because every country in the world has at least one of these colours on their national flag. Another idea sees in each colour a certain continent, for example, blue colour symbolizes Europe, yellow- Asia, red – America, black – Africa and green – Australia. The Olympic Games have been held in many countries, and Russia is no exception. In 1980 the 22nd Olympic Games took place in Moscow, and in 2014 they took place in Sochi.