Human beings have lived on this earth for at least two million years. For most of that time people did not live in towns. Sometimes they used to camp in caves. Sometimes they used to build camps in the forest or on open ground. These camps were just groups of simple houses that were made of branches and leaves or grass.
Only about thirty people lived in each camp. The men used to go hunting while the women and children collected food from the trees and other plants around the camp. All the food was shared between everyone in the group. After a few weeks they moved to another place in order to find more food there. It was a simple life, but people had to be clever. They had to make everything that they needed, and they had to know a lot about plants and animals. Man's body and brain were formed by his kind of life.
Nowadays a lot of people live in big towns and cities, and they work in offices and factories. Life is a lot easier than it was in the old days. There are fewer dangers, but there is less excitement. Most people do not have to hunt for food, but they have to stay in one place for most of their lives. They get some excitement from sport and films, but many of them feel that modem civilization is too unnatural. A few of them go looking for adventure--sailing round the world, climbing mountains, or exploring caves. Most people look forward to the holidays, because then they can
enjoy a change. A lot of them go camping in the country, or by the sea. They try to get back to nature. They try to live as people did thousands of years ago. But they also take a lot of modern luxuries with them. Camping today is very different from camping in the old days.
解析
Which of the followings is not a material of which camps were made?
细节题。从These camps were just groups of simple houses that were made of branches and leaves or grass．可知古时人们用树枝、树叶和草扎营，所以排除的D即为答案。