“市场上流通的纸币，既不是越多越好，也不是越少越好。”这是因为(   )

阅读理解

    Tom,Bill and Dave lost their backpacks．They are at the lost and found office．The backpacks are the same(相同的),but the things in them are different．Can you help them find the right(正确的)backpack?

    Tom：I have a  maths book and a pencil case in my backpack．There are three pencils,a pen and an eraser in the pencil case．

    Bill：I have a Chinese dictionary,a maths book and two notebooks in my backpack．

    Dave：There are two CDs,three picture books in my backpack．My English book is also in it．

国务院印发《关于国家应对气候变化规划（2014—2020年）的批复》提出，要确保实现到2020年单位国内生产总值二氧化碳排放比2005年下降40%－45%，这要求我们（   ）