根据短文理解，从A、B、C、D四个选项中选择正确答案填空。
As we all know, the environment around us is getting worse and worse. In some places we can't see fish 1 in the river or trees on the hills. Some people even have no clean water to drink.
Recently, a new lifestyle called low carbon life is 2 every corner of our country. The meaning of low carbon is 3 energy and no waste. It is such an important project that I can't wait 4 my ideas on how to promote it.
First, we should 5 a no-car day every week in our school. Because cars not only cause serious air pollution but also waste energy. 6 the no-car day, neither students 7 teachers are allowed to drive to school. At the same time, just walk or run. Use our 8 and enjoy the fun.
Second, we had better not use plastic bags 9. No one can stand the “white pollution”, 10 it is wise to use cloth bags which can 11 again and again.
12, one thing 13 we should keep in mind is that every big thing comes from the small details. So, as students, we ought to turn 14 the lights the moment we leave, use 15 sides of the paper, and reuse our textbooks and so on.
All in all, it weighs greatly for all of us to put the low carbon lifestyle into practice. Just set our mind to these: no-car days, no plastic bags, and no waste. Let's do it now.
>b 
，则实数a，b应满足的条件是