Answer:
The correct answer is - combined with hemoglobin.
Explanation:
The oxygen that is inhaled by the organism to the lungs from the environment is taken from the lungs to the different body tissues through the blood for performing cellular respiration and get energy.
The blood contains hemoglobin which is an iron-containing metalloprotein that carries the oxygen in red blood cells of the blood to the different body tissues from the gills or lungs. This oxygen transport iron-containing protein present in almost all the vertebrates.
Thus, the correct answer is - combined with hemoglobin.