I have a pencil case. It is nice and big. It has many colours. There are two blocks on my pencil case. One is yellow, the other is orange. In my pencil case, there are pens, pencils, a ruler and an eraser. I like my pencil case very much
如图是同学们探究“平面镜成像特点”的几种情境。下列说法正确的是( )
计划生育是( )①社会主义初级阶段的一项基本国策 ②以人口的发展一定要与经济社会发展相适应为依据③目前条件下解决我国人口问题的正确途径 ④实现可持续发展的正确选择