但是人们当时还不知道如何建造房屋。

　　Not a pleasant thought, since at that time it was often intensely cold – at certain periods far colder than today.

　　一想到这点令人很不愉快，因为在这个时期天气常常很冷——有时候甚至比现在冷得多。

　　Winters were longer and summers shorter.

　　当时冬季更长，夏季更短。

　　Snow lay deep throughout the year, not only on mountain tops, but down in the valleys as well,

　　从山顶到深深的谷底，终年覆盖着积雪，

　　and glaciers, which were immense in those days, spread far out into the plains.

　　还有像今天一样巨大的冰川远远向前推进至平原。

　　This is why we say that the Stone Age began before the last Ice Age had ended.

　　所以我们说石器时代开始早于最后一个冰河时代。

　　Prehistoric people must have suffered dreadfully from the cold,

　　史前时期的人类一定受了严寒之苦，

　　and if they came across a cave where they could shelter from the freezing winds, how happy they must have been!

　　如果他们偶然发现一个能给他们挡风御寒的山洞，他们一定会高兴！

　　For this reason they are also known as 'cavemen', although they may not have actually lived in caves.

　　因为这个原因，他们也被称为为“穴居人”，虽然他们可能实际上没有住在洞穴里。

　　Do you know what else these cavemen invented?

　　你知道这些穴居人还发明了什么吗？

　　Can't you guess? They invented talking.

　　你会想得到吗？他们发明了说话。

　　I mean having real conversations with each other, using words.

　　我指的是互相用词语进行真真正正的交流。