A、Wars. B、Pollution. C、Nuclear waste. D、Destruction of wildlife. A

Most people are aware that the earth is a delicate thing, and that it cannot last forever, if we do not take care of it. Apart from the dangers of blowing each other up, there is the problem of pollution of the environment, and the destruction of wildlife by hunters.
    Many species of whales, for example, are in danger of extinction because of hunters who continue whaling despite the world’s attempts to limit the annual catch. Seals are also threatened: and with the increasing use of nuclear power to generate electricity, a new danger has arisen: the pollution of oceans by nuclear waste.
    The Greenpeace organization exists to draw our attention to these problems. Its aim is to protect the environment and maintain the balance of the nature. It takes direct actions to prevent the killing of whales and seals, and to stop the dumping of nuclear waste at sea.
    As well as actually hindering activities in these areas, it exerts diplomatic pressure to persuade governments to pass new laws to make these things illegal.
Questions 16 to 20 are based on the passage you have just heard.
16. What does the speaker mean by saying "the earth is a delicate thing"?
17. Why are many species of whales in danger of extinction?
18. Why is the earth faced with a new danger with the use of nuclear power to generate electricity?
19. Which kind of danger to the earth has not been mentioned by the speaker?
20. What is true of the Greenpeace organization?