Ten years ago, when environmental lawyer Kassie Siegel went in search of an animal to save the world, the polar bear wasn’t at all an obvious choice.Siegel and Brendan Cummings of the Center for Biological Diversity in Joshua Tree, Calif., were looking for a species whose habitat was disappearing due to climate change, which could serve as a symbol of the dangers of global warming.Her first candidate met the scientific criteria—it lived in ice caves in Alaska’s Glacier Bay, which were melting away—but unfortunately it was a spider.You can’t sell a lot of T shirts with pictures of an animal most people would happily step on.

　　Next, Siegel turned to the Kittlitz’s murrelet, a small Arctic seabird whose nesting sites in glaciers were disappearing.In 2001, she petitioned the Department of the Interior to add it to the Endangered Species list, but Interior Secretary Gale Norton turned her down.Elkhorn and stag horn coral, which are threatened by rising water temperatures in the Caribbean, did make it onto the list, but as iconic species they fell short insofar as many people don’t realize they’re alive in the first place.The polar bear, by contrast, is vehemently alive and carries the undeniable charisma of a top predator.And its dependence on ice was intuitively obvious; it lives on it most of the year.But it took until 2004 for researchers to demonstrate that shrinking sea ice was a serious threat to the bears’ population.On Feb.16, 2005—the day the Kyoto Protocol to curb greenhouse-gas emissions took effect, without the participation of the United States—Siegel petitioned to list polar bears as endatrgered.Three years later her efforts met with equivocal(不明确的) success, as Interior Secretary Dirk Kempthorne designated the bears as “threatened” (not endangered), a significant concession from an administration that has stood almost alone in the world in its reluctance to acknowledge the dangers of climate change.The Endangered Species Act (ESA), whose odd lists of snails and bladderworts sometimes seemed stuck in the age of Darwin, had been thrust into the mainstream of 21st-century environmental politics.Break out the T shirts!
The passage is focused on _____.

A.how the scientists tried to protect endangered species

B.how the symbolic endangered species has been chosen

C.the relation between global warming and endangered species

D.the problems in and the future of endangered species protection