如图所示，m₁=2kg，m₂=3kg，连接的细线仅能承受1N的拉力，桌面水平光滑，为使线不断而又使它们一起运动获得最大加速度，则可以施加的水平力F的最大值和方向为（   ）

阅读下面短文, 掌握其大意, 然后从所给的四个选项中, 选出一个最佳答案。

    Here is a picture of my 1. I like it very much. It's always very 2. We have a soccer in 3 classroom, but you can't see it. It's under the 4 desk. You can see a map of China and 5 pictures on the walls. My classmates and I draw（画） the pictures. We like our art teacher-Mr Brown very much. He is 6 the USA. But now He is in China with his family . He likes playing 7. After school he often plays basketball with my 8. He likes  9, because he 10 music can make him relaxing.

词语理解（解释词语）

①军阀：

②轻易：

③恐怖：

④一拥而入：

水是人类必不可少的宝贵资源，是一切生物体的最基本组成成分．回答问题

（1）下列净化水的方法中，净化程度最高的是　____ （填序号）；

A．吸附    B．沉淀    C．过滤    D．蒸馏

（2）电解水时，用____来检验图B试管中的气体．