多亏有了绿色植物，空气中充满了游离氧。
It is thanks to the green plants that the air is full of free oxygen.
对微弱的电场而言，空气是优良的绝缘体(电子附著到氧原子上的速度，大于受冲撞而游离的速度)，并不会有可观的电流流通。
For small fields, air is a good insulator-electrons attach to oxygen atoms faster than they are knocked loose by collisions-and electric current cannot flow in any appreciable amount.
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