After hydrogen and oxygen, which element makes up almost all of the most common substances in your body?

By weight, oxygen makes up approximately 65% of the human body. Numerically, hydrogen approaches 65% of the total number of atoms in the human body, but it is … probably closer to 63% for most people. Accounting by Mass: The mass of the human body is provided mostly by oxygen, carbon, hydrogen, nitrogen.

Hydrosphere is the correct answer