A、It collapsed at least once in the past 1. 3 million years. B、It sits firmly on solid rock at the bottom of the ocean. C、It mel

Among global warming’s most frightening threats is the prediction that the polar ice-caps will melt, raising sea level so much that coastal cities from New York to Los Angles to Shanghai will be flooded.
    Scientists agree that key player in this scenario is the West Antarctic ice sheet, a Brazil-size mass of frozen water that is as much as 7, 000 feet thick. Unlike floating ice shelves which have little impact on sea level when they break up, the ice sheet is anchored to bedrock well blow the sea surface. Surrounded by open ocean, it is also vulnerable, but Antarctic experts disagree strongly on just how unstable it is.
     Now, new evidence reveals that all or most of the west Antarctic ice sheet collapsed at least once during the past 1. 3 million years, a period when global temperatures probably were not significantly higher than they are today. And the ice sheet was assumed to have been stable. In geological time, a million years is recent history. The proof, which was published last week in Science, comes from a team of scientists from Uppsala University in Sweden and the California Institute of Technology who drilled deep holes near the edge of the ice sheet. Within samples collected from the solid substance lying beneath the ice,they found fossils of microscopic marine plants which suggest that the region was once an open ocean, not solid ice. As Herman Englehart, a co-author from the California Institute of Technology says, "the West Antarctic ice sheet disappeared once, and can disappear again. "
26. Q: What is one of the most frightening threats of global warming according to the passage?
27. Q:What did scientists disagree on?
28. Q:What does the latest information reveal about the West Antarctic ice sheet?
29. Q:What does the scientists’ latest finding suggest?