Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the following questions.

The environment is everything around us, both natural and made by man. A major problem in the world today is the destruction of the natural environment. This is a complicated problem.

We burn fuels, and this causes air pollution. We throw away plastic bags, containing toys and other objects. Unlike paper and wood, they will exist long in the environment. We have made thousands of new chemicals. Factories that make or use chemicals always have chemical wastes. These are often poisonous, and they also stay in the environment.

Since 1945, several countries have been testing nuclear bombs in the air and underground. The explosions in the air cause nuclear fallout. The fallout causes cancer and kills animals and people. Nuclear power plants that make electricity also produce dangerous wastes and have accidents that can be very disastrous.

What is the main idea of the passage?