[单项选择]Speaker A: Sam, I'm calling to say goodbye to you, as I'm leaving this afternoon.Speaker B:______

Say goodbye to the Mountain Gorilla. Say farewell to the Short Tailed Chinchilla.
That’s the conclusion of the United Nations Environment Program’s (UNEP) Third Global Environmental Outlook Report. The report was compiled (编写) for the UN from the work of 1 100 scientists. It predicts the state of the planet in the year 2032 based on the policies and practices of the last 30 years. If these continue, UNEP says, we’re going to be living on a very lonely planet. By 2032, one quarter of the world’s mammal species (哺乳动物种群) will disappear. They will be joined by 12% of the world’s bird species. And according to UNEP, 5 611 species of plants will also be wiped out-but since only 4% of the world’s plant species have been examined in detail, that figure will probably be much higher.
UNEP blames a variety of causes, from poverty and overpopulation to pollution, global warming and profit-driven economic and trade policies. But ther
A. National parks.
B. Global warming.
C. Overpopulation.
D. Chemicals.