下列四幅表示地球绕日公转的示意图，正确的是（　　）

根据短文内容，判断正误。

    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.

根据短文理解，从A、B、C、D四个选项中选择最佳答案填空。

    Do you know how to study 1 and make your study more effective ( 有效的)? We all know that Chinese students usually study very hard for long 2. This is very good, but it doesn't 3 a lot, for an effective student must have enough sleep ,enough food and enough rest and 4. Every day you need to go out for a walk or visit some friends or some nice places. It's good for your 5.

    When you return  6 your studies, your mind will be refreshed(清醒)and you'll learn more 7 study better. Psychologists (心理学家) 8 that learning takes place this way. Here take English learning 9  an example. First you make a lot of progress and you feel happy. Then your language study seems 10 the same. So you will think you're learning  11 and you may give up. This can last for days or even weeks, yet you 12 give up, and at some point your language study will again take another big 13. You'll see that you really have been learning all along. If you get enough sleep, food, rest and exercise, studying, English can be very effective and  14. Don't give up along the way. Learn 15 you are sure to get a good result.