1.沙化問題日趨嚴重;
2.沙化問題成因;
3.解決辦法。
[寫作導航]可先用數位說明世界沙化的問題，然後指出每年沙漠面積還在擴大，並預計其嚴重後果;接著可分析造成沙漠擴大的原因，一是大自然本身造成的，如某些地方少雨;二是人為因素造成的，如過度放牧、耕作、砍伐、開採等;最後如建立綠化帶等。
[範文]
There are vast areas of land on every continent where there is no rainfall or vegetation. It is estimated that more than 40 per cent of the land on the earth's surface is desert or desert-like. What is worse, these deserts are spreading at a surprising rate every year. If this trend continues, sand will bury almost everything in the near future.
Two reasons account for the fact that deserts are spreading. The first reason comes from nature. These areas are usually located in the far inner land where rainfall can never reach. The second reason comes from man himself. Many people regard immediate profit as a supreme value, which results in over-grazing, poor farming, tree cutting, and strip mining. All these activities leave land unprotected. Consequently, rain water washes away topsoil into rivers and oceans, wind blows away loose soil.
The expansion of deserts must be stopped if we are to survive on this planet. Man can make deserts, he can also prevent them from spreading. Stopping over grazing, poor farming, tree cutting, and strip-mining is the first step. Planting a green belt of trees along the edge of deserts is the second step. Covering the deserts with vegetation is another step. We hope man can make great efforts to develop better ways to bring the spreading deserts under control