Alongside oxygen and hydrogen, what is the other element that accounts for the vast majority of living matter?

carbon is also plant food, specifically carbon dioxide, and is not a pollutant as some would try to espouse.

Basis of Organic Chemistry

Player #6616037, Carbon bonds well to itself and to other elements. So it enables the complex combinations necessary for life.

Player #6616037, sugar, when H, C and O combine.

Player #6616037, sugar among a multitude others!

If oxygen & hydrogen can produce the components of water (H2O),what does the carbon do?