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.
当钻井平台下沉时，立管在顶部附近的地方断裂，同时另一端仍与底部的防喷器相连。
When the rig sank, the riser broke near the top while remaining attached to the blowout preventer at the bottom.
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