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.