I believe the answer is C
I hope you get it right and have a great day :)
I believe it’s carbon dioxide, because you use your respiratory system to breathe in oxygen, and oxygen goes through your circulatory system. And you breathe out CO2.
Malnutrition is not having enough of the needed nutrients (not having a good diet, eating a lot of unhealthy food but still eating) this could be from either under consumption or over consumption. While under-nutrition is when someone eats an inadequate amount of food for an extended period of time (not eating enough food in general).