Read the following extract and answer the questions Environment implies a healthy natural balance in the air, water, animals, plants, and other natural resources. It contributes to the existence and development of organisms but does the opposite if pollution occurs. Pollution is the process of creating the environment dirty by adding harmful substances into it. Industrialization and other anthropogenic activities constantly pollute the environment and harm nature, posing serious threat to the existence of mankind. The increase of world population implies growth of industries, and industrial units release toxic gases and filthy poisonous effluents. Besides, trees are cut down for fuel, various commercial purposes, and building houses, reducing the supply of oxygen. Consequently, the shelter of birds and other animals is destroyed and ultimately the ecological balance is upset. Therefore, environment saving scientific methods should be adopted in development activities and environment protecting rules and regulations need to be enacted towards reducing emissions of toxic gases and poisonous effluents.