二氧化碳是一种常见的气态物质。

Carbon dioxide is a common ___gaseous substance.

水沸腾时会变成气态。

Water turns into a ___gaseous state when it boils.

他的承诺像烟雾一样虚无缥缈，没有任何实质内容。

His promises were as ___gaseous as smoke, with no real substance to them.