Task: Sentence Ordering
Input (English): Steps: (1) The human body takes a breath inward (2) Air is transported to the lungs (3) Air reaches the alveoli, the smallest air sacs in the lungs (4) In the alveoli, air passes into the blood within small capillaries (5) The dissolved oxygen is picked-up by red blood cells (6) The red blood cells bind the oxygen via a protein called heme (7) Red blood cells circulate throughout the body and reach the various tissues (8) Within small capillaries, the heme release the oxygen (9) The oxygen can then reach the cells within the tissue  
Where does the following step fit into the given list of steps: The gaseous oxygen in the air dissolves into the capillary blood 
Output (English):  After step 4.