題組21~28克漏字：
         There are deserts all over the world. People can find them in Africa, China, South America, and North America. In some places,   21.    . This is a big problem because people can’t plant anything in deserts and   22.     animals can live there. Once there are more and more deserts, the useful land for people and animals will   23.     less and less.
         However, besides nature, people cause deserts to grow, too.   24.     does it happen? The first cause is air pollution. It can make a place hotter, so the land will become   25.    . Second, too many people or animals living in a place can also harm the land.   26.    , trees can keep water in the ground, so when people cut down trees, less water stays in the ground, and the quality of the land becomes lower.
           27.     help stop deserts from growing faster in the future? Join us. Try to plant more trees and   28.    . We need to do our best to give our children a better land to live.
【題組】21.
(A) people live in deserts
(B) animals die in deserts
(C) deserts are growing
(D) deserts becomes wetter