听力原文：M: Hey, Jane. What's so interesting? W: Oh, hi, Tom. (19)I'm reading this fascinating article on the societies of the Ice Age during the Pleistocene period. M: The Ice Age? There weren't any societies then, just the bunch of cave people. W: That's what people used to think. (20)But a new exhibition at the American Museum of National History shows that Ice Age people were surprisingly advanced. M: Oh, really? In what ways? W: Well, Ice Age people were the inventors of languages, art and music as we know it. And they didn't live in caves. They built their own shelters. M: What did they use to build them? The cold weather would have killed almost all the trees, so they couldn't have used wood. W: In some of the places with warmer climate, they did build houses of wood. In other places, they used animal bones and skins or lived in natural stone shelters. M: How did they stay warm? Animal skin walls don't sound very sturdy. W: Well, it says here, that in the early Ice Age, (21) they often faced their homes towards the south to take advantage of the sun, a primitive sort of solar heating. M: Hey, that's pretty smart. W: Then people in the late Ice Age even insulated their homes by putting heated cobble stones on the floor. M: I guess I spoke too soon. (22)Can I read that magazine article after you've done? I think I'm going to try to impress my anthropology teacher with my amazing knowledge of Ice Age civilization. (23)