当志愿者在正常的空气中、纯氧的环境下，或者混有超过正常的二氧化碳含量的空气中呼吸时，他们被要求要想着打哈欠。

Volunteers were told to think about yawning, while they breathed either normal air, pure oxygen, or an air mixture with an above-normal level of carbon dioxide.

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当志愿者在正常的空气中、纯氧的环境下，或者混有超过正常的二氧化碳含量的空气中呼吸时，他们被要求要想着打哈欠。

Volunteers were told to think about yawning while they breathed either normal air, pure oxygen, or an air mixture with an above-normal level of carbon dioxide.

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许多环境专家现在认为，甲烷比二氧化碳对全球变暖负有更大的责任。

Many environmental experts now believe that methane is more responsible for global warming than carbon dioxide.

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She needs to know this enzyme works by both acid base chemistry, and oxidation reduction.

她要知道酶催化，她需要知道这种酶,在酸碱环境下的反应和氧化还原反应。

麻省理工公开课 - 化学原理课程节选