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．

2NH₃（g）+CO₂（g）═CO（NH₂）₂（s）+H₂O（g）

小明不爱吃蔬菜，最近几天，每次刷牙时，牙龈都出血，他可能患了（　　）

在某草原生态系统中，草、鼠、兔、狐、狼（饥饿的狼、狐也捕食鼠）五类生物可构成一个简单的食物网，试绘出这一食物网，并回答问题：