Answer:
Carbon, Oxygen, Hydrogen And Nitrogen - Have In Common? They All Have The Same Number Of Valence Electrons. They All Have Unpaired Electrons In Their Valence Shells. They Are Elements Produced Only In Living Cells.
Integumentary system I believe
When blood is in the lungs,
where oxygen is plentiful, oxygen easily binds to the first subunit and then quickly fills up the remaining ones. Then, as blood circulates through the body, the oxygen level drops while that of carbon dioxide increases. In this environment, hemoglobin releases its bound oxygen.
