A、No melting has been observed recently. B、The past several winters have been unusually severe. C、Nothing unusual has happened i

M: Doctor White. (19)we recently learned that a large piece of the Larsen Ice Shelf in Western Antarctica broke off in early January. Could you please tell us exactly what happened?
W: I’d be happy to. The piece that broke off was over a thousand square miles in area. More recently and quite alarming to scientists is that the 40-mile crack, some 30 feet wide in places has torn through the ice shelf.
M: I understand that the Scientific Community is quite concerned. What is the significance of these events?
W: Well, (20)some scientists believe that this is a clear sign of global warming. Back in 1978, some American researchers predicted that Antarctica would show early signs of global warming due to the greenhouse effect.
M: But couldn’t crumbling ice shelves also be a result of the unusual weather Antarctica itself has experienced lately?
W: That’s certainly possible. (21)But you have to remember that over the past thousands of years, ice shelves have been through a lot of weather changes without breaking-up. Remember too that although ice shelves float on the ocean, they are attached to the continent and can be as thick as a thousand feet.
M: I think most people know that if the ice cap over Antarctica melts, the level of the oceans will rise. What sort of impact will this have?
W: Well, (22)the ice shelves currently insulate the Antarctic continent from wind, which slows down melting. But without ice shelves to cool the wind, it would be warmer than usual as it flows over Antarctica. If the winds cause even a tenth of the continent’s ice to melt, the world’s oceans could rise as much as 30 feet.
19. Q: What are the speakers mainly discussing?
20. Q: Why are the events of ice cracking important?
21. Q: Why does the woman doubt that weather is responsible for the recent events?
22. Q: Why are the ice shelves important to the Antarctic?