根据短文内容及首字母提示，填写所缺单词，使短文意思完整。每空限填一词。

Long ago, the early people did not live in houses as we do today. Most of the homes were in caves or shelters (遮蔽物) which were built in trees. These ‘homes’ were only used as temporary (临时的) shelters to p____1____ them from the sun, the rain and the wild animals in the forests. Men of that time were called ‘cave people’.

These ‘cave people’ usually lived in small groups and life was not e____2____ for them. They had to move from place to place to s____3____ for food. They would hunt, fish or pick wild fruit. When they couldn’t find a____4____ to eat, they would leave to find another proper place. Their tools were very simple. They ate raw (生的) food u____5____ they learnt how to make a fire. For clothing, they used only the bark (树皮) of trees or the skins (皮) of animals to c____6____ their bodies.

However, the lives of the ‘cave people’ changed. They collected the seeds (种子) of wild plants that g____7____ in the forests. Soon they learnt to plant fruit, vegetables and other crops. They also kept cows, sheep and other kinds of farm a____8____ for milk, meat and skins. They became f___9___ and lived in only one certain area. Their groups became l____10____ than before as they lived more settled (固定的) lives. They built houses as long-lasting homes, and as a result, villages and towns developed quickly. The ‘cave people’ began to be civilized (文明的).