国家对资本主义工商业的社会主义改造采取的主要措施是（　　）

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    Forests have always been useful and important to men who make use of them in many ways. Every day trees are serving man everywhere. Trees supply man with fruits and building materials in the form of wood. Without trees it would be impossible to build houses, boats, bridges and so on. Furniture such as desks, chairs and beds is made of wood. Trees can stop man from the terrible heat. They're also useful in preventing(阻止) good and rich top soil from being washed away during heavy rains. If there were no forests, heavy rains would wash away the rich surface(表层) soil that is so important to plants. The result is that the land will become a desert. There are plenty of desert areas in the world. A long time ago these desert areas used to be very rich areas, but men in the past had no enough knowledge about science of nature, and they cut down too many trees in the area where they lived and never planted new ones. By and by, the rich surface soil was blown and washed away by strong winds and heavy rains. In the end the rich land changed into useless deserts where nothing could grow.