Activation energy - is the minimum quantity of energy that the reacting species must possess in order to undergo a specified reaction.
The right answer is He is studying oxygen, which can also be found in proteins.
Carbon atoms could also be a right answer if there was a statement...
Sugars, composed only of carbon atoms, hydrogen, and oxygen, are the simplest energetic nutrients. Example to (C6H12O6): If we look at the chemical formula for glucose, we can see that the proportion Hydrogen / Oxygen corresponds to that of water (H2O)
Lipids also consist of carbon atoms (C), hydrogen (H) and oxygen (O), but fatty acids are molecules that are low in oxygen. Example: Linoleic acid C18H32O2