听力原文：M: Hello. This is Greg Rice reporting live in Barrow. Alaska.
W: Hello. Greg. Is everything going smoothly？
M: Yes. I've just arrived here in Barrow. Alaska, to bring you live coverage of what appears to be the results of a huge meteorite impact, perhaps the largest in recent history, that occurred just twelve hours ago. The exact location of the impact is unknown, but estimates put it about 20 kilometers south of Barrow based on shock waves felt throughout the region.
W: Are there any witnesses？
M: Yeah. Some witnesses say they saw a bright light streaking through the sky, accompanied by a mating boom, moments before the impact. It's unknown whether there are any casualties, but it is unlikely considering this sparsely populated area.
W: It's said that such impacts were commonplace during the formation of our solar system, and many believe that a meteorite 10 kilometers in diameter which crashed into Earth 65 million years ago led to the mass extinction of many animal species including the dinosaurs.
M: You're right. But R is often difficult to calculate the number of such large impacts on Earth because erosion and vegetation make it difficult to spot them. In recant years, astronomers have focused more of their attention on the paths of many uncharted space rocks or asteroids floating out there in the hope that we might be able to determine the threat they pose on mankind...This is Greg Rice reporting from Alaska.
W: Thanks, Greg...We'll keep you up-to-date on any development there.
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An alien spacecraft landing.
B. The impact of a meteorite.
C. A volcanic eruption.
D. The blizzard conditions in Alaska.