听力原文：M: I really appreciate your filling in on yesterday's lecture. W: No problem. I thought you might want to go over it together. And, anyway, it helps me revtew. M: I am. Thanks. So, you said she talked about squid? Sounds a little strange .... W: Well, actually, it was about the evolution of sea life — a continuation from last week. The octopus and the squid descended from earlier creatures with shells. They survived by shedding their shells—somewhere between 200 and 500 million years ago. M: That's a pretty long span of time. W: I know. That's what she said, though. To be precise: 'Exactly when they emerged is uncertain...and why is still unexplained.' M: Some squid are really huge. Can you imagine something that big ifit still had a shell? W: Actually, it's because they lost their shells that they could evolve to a bigger size. M: Make sense. But some are really huge. I've read about fishermen that caught squid that weighed over a ton. Did she talk about how that happens? W: Not really. But she did mention some unusual cases. In 1933 in New Zealand they caught a squid let's see here it was twenty-two yards long. Its eyes were eighteen inches across. Can you imagine? M: Reminds me of all those stories of sea monsters. (20)