A、They lived in large groups. B、They used sand as insulation. C、They kept fires burning constantly. D、They faced their homes tow

M: Hey, Jane. What’s so interesting?
W: Hi, Tom. I’m reading this fascinating article on the societies of the Ice Age.
M: (19)The Ice Age? There weren’t any societies then, just a group of people living in the cave.
W: That’s what people used to think. But a new exhibit of the America museum of natural history showed Ice Age people were surprisingly advanced. You may never hear of it.
M: Oh, really? In what ways?
W: (20)Well, Ice Age people were the inventors of language, 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 off most of the trees so they couldn’t have used wood. Of course they couldn’t live in the ice blocks.
W: In some of the warmer climate, they did build the 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 wails don’t sound very sturdy(坚固的).
W: (21)Well, it says here that in the early Ice Age, they often faced the house towards south to take the advantage of the sun, a primitive sort of solar heating.
M: Hey, that’s pretty smart. But when night comes, it is still a problem to keep warm.
W: They had some solution. People in the late Ice Age even insulated their homes by putting heated stones on the floor. They also have some creative ways to make their life better.
M: All these sound interesting. (22) Can I read that magazine article after you’re done? I think I can use some of the knowledge for my recent paper.
W: Yes, sure.