Food is very important to our health. Everyone needs to eat well if he or she wants to have a strong body.
Our minds, like our bodies, always need the best food. This kind of food is knowledge. We start getting knowledge when we are very young.

空气污染的主要来源是(   )

我是拼音小能手

脑袋____  无影无踪____ 智慧老人____   

 究竟____   捞回机舱____   维修____

某经销商销售一种产品，这种产品的成本价为10元/千克，市场调查发现，该产品每天的销售量y（千克）与销售价x（元/千克，且10≤x≤18）之间的函数关系如图所示；

如图所示是一种环保型手电筒，使用它时只要将它来回摇晃，就能使灯泡发光．下列四幅图中能反映这种手电筒的工作原理的是（　　）