氧气和氢气都是对生命和工业至关重要的气体。

Oxygen and hydrogen are both important ___gases for life and industry.

二氧化碳是一种导致全球变暖的气体。

Carbon dioxide is a ___gas that contributes to global warming.

天然气常用于家庭供暖和烹饪。

Natural ___gas is commonly used for heating homes and cooking.