21、You may think there is only sand in the desert of the world, but it is not true. In the desert, as we know, there is a little rain and it is not _ _ _ 21 _ _ _ for most plants. Still we can see some plants live in the desert.
There is water in some places in the deserts. We call these places oases(绿州). In the oases, there are villages and towns. People grow all kinds of vegetables and rice in the fields there. People _ _ _ 22 _ _ _ live outside the oases. They have camels, sheep and other animals. These animals live _ _ _ 23 _ _ _ the desert plants for their food and do not need any water. The animals are useful to the desert people in many ways. They eat the meat and drink the milk of the animals. They use the camels for carrying water, food, and something else.
The people of the desert have to keep _ _ _ 24 _ _ _ from place to place. They must always look for grass or desert plants for their animals. When there is no more food for their animals, they move to another place. The desert people are _ _ _ 25 _ _ _ . Every one in the desert likes to help the people in trouble and give them food and water.