阅读理解。
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.
根据短文内容,判断正(T)误(F).
( )1. Trees are not serving man everywhere.
( )2. Without trees it would be possible to build houses, boats, bridges and so on.
( )3. Trees can stop man from the terrible heat.
( )4. There are few desert areas in the world.
( )5. In the end the rich land changed into useless deserts where nothing could grow.
3C(g)，若反应开始时充入2 mol A和2 mol B，达平衡后A的体积分数为a%。其他条件不变时，若按下列四种配比作为起始物质，平衡后A的体积分数大于a%的是[ ]