车库里的汽车引擎运转时会产生无色无味的一氧化碳，所以车库要保持通风。

Running car engines in the garage produce ___carbon monoxide, so proper ventilation is essential.

使用燃气热水器时要保持通风，防止一氧化碳中毒。

Keep the room ventilated when using a gas water heater to avoid ___carbon monoxide poisoning.