【正确答案】 C

【答案解析】原文：For the first time ever, scientists have recorded the heart rate of the world’s largest creature: the blue whale. To get this reading, they attached an electrocardiogram device to the body of a whale. They found that the mammal’s heart rate can slow to just two beats a minute as the animal searches for food below the surface of the ocean. The highest heart rate they recorded was 37 beats a minute after the whale returned to the surface for air.题目问为什么白水冰川被称为第三极。新闻中提到“The huge body of ice is in the southeastern edge of a Central Asian region called the Third Pole.It is about 4.5 million square kilometers in area and holds the world’s third largest collection of ice after Antarctica and Greenland”,即位于中亚地区的东南边缘的巨大冰体被称为第三极。白水冰川的面积约为450万平方千米，拥有仅次于南极和格陵兰岛的世界第三大冰藏,故选C。