概念模型是将现实世界的客观对象抽象为某一种信息结构，它并不依赖于计算机系统，它的基本

儿童能以命题形式思维，则其认知发展已达到（）。

A．感知运动阶段

B．前运算阶段

C．具体运算阶段

D．形式运算阶段

如图，取一个瓶口内径略小于乒乓球直径的雪碧瓶，去掉其底部，把一只乒乓球放到瓶口处，然后向瓶里注水，会发现水从瓶口流出，乒乓球不上浮。若用手指堵住瓶口，不久就可观察到乒乓球上浮起来。此实验说明了

A、大气存在压强        

B、连通器原理

C、浮力产生的原因    

D、液体的压强与液体的密度和深度有关

Hi, I’m Xin Yue. I am 15 years old. I study at Monte Vista Christian School in California, US. The school ife in America is 小题1:  from that in China. I’d like to   小题2:  you something about my school life in America.

I took many textbooks to school in China. But in America, I usually take one thing    小题3:  me--- an iPad.

Every student at my school uses an iPad for study. We rent them from the school,  小题4:   costs about $ 100. We can use them for three years.

 小题5:  we have classes, we download textbooks and other teaching materials online with our iPads. We can not only read the electronic books,    小题6:  also listen to music or watch videos in class. It makes our study full of fun.

But they also bring us some    小题7: . Some of my classmates play games or do other things in class.

I think if we have good self-control, iPads can be very helpful. Do you   小题8:    with me?

结合诸条约内容简述中国社会沦为半殖民地半封建社会的过程。

班主任应怎样组织和培养班集体