If the theory was correct, breathing air with extra carbon dioxide should have triggered yawning, while breathing pure oxygen should have suppressed yawning.
如果这个理论是正确的，那么吸入含有额外二氧化碳的空气应该会引起打哈欠，而吸入纯氧应该可以抑制打哈欠。
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.
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.
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。
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