The size and location of the world's deserts are always changing. Over millions of years, as climates change and mountains rise, new dry and wet areas appear. But within the last hundred years deserts have been increasing after frightful speed. This is partly because of natural changes, but most responsible for creating deserts are men. Man can make deserts, but they can also prevent them from getting bigger. Algeria is planning a green belt of trees along the edge of the Sahara Desert to stop the sand. In China, too, _ are being built in the northwest to keep the desert from growing. But desert still threaten the world. Experts believe that land that is on the way to becoming deserts equals the size of Australia, Russia and US put together. Can we stop the spread of the world's deserts and save the land that is so essential to mankind? Yes, we can, and we must. The word "windbreaks" means _ A) high walls as a belt to stop the wind B) trees planted as a belt to stop the wind C) long and deep ditch as a belt to stop the wind D) men stood side by side as a belt to stop the wind
B