A、They refute current scientific theories. B、They have destroyed research facilities. C、They could be a sign of global warming.

M: Dr. White, we’ve recently learned that a 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 happy to. The piece that broke off was over a thousand square miles in area. More recently, and quite alarming to scientists, is that a forty-mile crack, some thirty 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, 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, you know, the process of heat being trapped at the surface of the Earth by the atmosphere.
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, 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.
W: If the winds cause even a tenth of the continent’s ice to melt, the world’s oceans could rise as much as thirty feet.
Questions 19 to 22 are based on the conversation you have just heard.
19. What are the speakers mainly discussing?
20. Why are the events important?
21. Why doesn’t the woman believe that weather is responsible for the recent events?
22. What would be the likely result of melting of the ice cap?