A、Ocean currents. B、Climate disorder. C、Human being. D、Natural disasters. C原文中有一处自问自答：“怨谁?科学家认为99％动植物面临灭绝的危险是因为人类活动。”故选C。

Some of the planet’s most precious animals and plants are disappearing, according to the World Conservation Union(IUCN).[16]The group, based in Switzerland, works with governments and experts to protect endangered species. On September 12, the IUCN released its Red List, a list of species at greatest risk of extinction. The list includes 41,415 animals and plants. The IUCN says that habitat destruction, hunting and other factors threaten one in four mammals, one in eight birds and one in three amphibians. Who is to blame? Scientists believe that 99 percent of threatened species are at risk because of human activity. "We are losing animals and plants at a high rate," says Julia Marton, Director General of the IUCN. "We need to change our behavior." Warmer oceans and over-fishing are affecting sea life. This year for the first time corals made their appearance on the list.[18]The gharial, a crocodile living in India and Nepal, has lost almost 60 percent of its population in the last 10 years. It is a victim of habitat destruction. Still, the news is not all bad. Thanks to efforts made to protect it, the Mauritius echo parakeet, a bird once endangered, has seen an increase in its population. "This shows that protection methods can work," says Marton. "That’s the message we want to send to young people."
16. What is the IUCN aimed at?
17. According to scientists, who is to blame for the endangered species?
18. Why does the speaker mention the crocodile living in India and Nepal?
19. What does the bird example show according to Julia Marton?