In order to function properly, your body needs
> oxygen
carbon dioxide
nitrogen
all of the above

your body needs oxgen most importantly. You exhale carbon dioxide not inhale it, so your body doesnt need that, nor nitrogen because it is a gas and we dont need gas to live.

Explanation:

before, trains worked using the steam engine. thus, it uses heat so it is crucial to apply heat balance. the steam engine absorbs energy during the stage of boiling water. so, this is the endothermic reaction. when the steam is used to work the piston, it has to release this energy through running the train. the excess energy is released as an exhaust to the chimney. this is the exothermic process because it releases energy to the surroundings.