Ecology is the study that helps to preserve the Earth, its plants and animals.at present times we have to face such ecological problems as acid rain, global warming, loss of rare species, ozone reduction, etc. Many scientists think that it is connected with industrial boom and development of civilization in the world. Another problem which is worth mentioning is the tree cutting. Trees are a source of oxygen and clean air. So, by doing this people simply violate the biological balance. All the above mentioned ecological problems are the result of man's careless interaction with nature.
1. When he returns to St. Petersburg, he will call) on us. 2. If I see) him, I will tell) him about their letter. 3. We will gather) at our place when my brother comes ) back from Africa. 4. I will sing this song with you if you ] tell) me the words. 5. I hope you will join) us when we gather) in our country house the next time. 6. What will you do) when you come home? 7. If I stay) some more days in your town, I will (call) on you and we have) a good talk. 8. He had gone to the Public Library very often when he was a student./ He will go to the Public Library very often when he is a student 9. As soon as I return) from school, I ( will ring) you up. 10. You will (to pass) many towns and villages on your way before you arrive) in Moscow. 11.i will stay) at home till she comes . Then we will (to go) to the theatre if she brings tickets. 12. After i finish) school, I will (to enter) the University
