在顶部和底部各留一点空隙，这样空气就可以流通了。
带正电荷的粒子集中在云团的顶部和底部，但中间区域形成的是带负电荷的粒子。
Concentrations of positively charged particles develop at the top and bottom of the cloud, but the middle region becomes negatively charged.
还请注意到面板顶部和底部的导航控件。
Also notice the navigation controls at the top and bottom of the panel.
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