Carbon dioxide in pure form can asphyxiate because it is heavierthanair.
因为二氧化碳比空气要重，纯净的二氧化碳可以使人窒息。
2
When carbon unites with oxygen, it forms a colorless, odorless, and tasteless gas called carbon dioxide, which is heavierthanair and will extinguish a flame.
当碳与氧结合形成一种无色、无味、无嗅的气体叫做二氧化碳，它比空气重，可以灭火。
3
But it is worth remembering that just over a century ago, heavier-than-air flight seemed an impossible dream.