Rewrite the sentences using reduced relative clauses. 1 Childcare is a subject which is often overlooked at school. 2 Students who are coming on the trip should be at school by 7.30. .3 First aid classes, which were introduced to the school last year, have been successful. .4 Students who are interested in joining the music club should complete the registration ХЕЕЕЛП

Chemical pollution of atmosphere.

The person pollutes atmosphere in the millenia, however consequences of the use of fire which it used all this period, were insignificant. It was necessary to be reconciled by that the smoke disturbed to breath and that soot laid down a black cover on a ceiling and walls of dwelling. Received heat for the person was more important, than pure air and incomplete walls of a cave. This initial air pollution did not represent a problem for people lived then small groups, occupying unreasonably extensive untouched environment. And even the considerable concentration of people in rather small territory as it was in a classical antiquity, was not accompanied still by serious consequences.

So was up to the beginning of the nineteenth century. Only for last hundred years development of the industry "has presented" us with such productions which consequence in the beginning the person could not present itself yet. There were the cities-millionaires which growth it is impossible to stop. All is result of great inventions and gains of the person.

The basic polluting substances.

Basically there are three basic sources of pollution of atmosphere: the industry, household boiler-houses, transport. The share of each of these sources in general, air pollution strongly differs depending on a place. Now that most strongly pollutes air industrial production. Sources of pollution - thermal power stations which together with a smoke throw out sulphurous and carbonic gas in air; the metallurgical enterprises, especially nonferrous metallurgy which throw out in air оксиды nitrogen, hydrogen sulphide, chlorine, fluorine, ammonia, connections of phosphorus, a particle and connection of mercury and arsenic; chemical and cement works. Harmful gases get to air as a result of burning of fuel for needs of the industry, heating of dwellings, work of transport, burning and processing household and industrial wastes.