随着顶部压力的解除，火山激烈喷涌出大股的岩石、灰尘、气体和蒸气，降落下来后覆盖了数百平方英里范围内的森林。

Relieved of the overlying pressure, the volcano ejected a blast of rocks, ash, gas, and steam that blew down and buried several hundred square miles of forest.

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为了把气体限制在一定的范围内，我们必须施加压力。

In order to confine a GAS we must apply a pressure.

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为了把气体限制在一定范围内，我们必须施加一个压力。

In order to confine a gas we must apply a pressure.

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