Task: Sentence Ordering
Input (English): Steps: (1) The oxygen passes through the bronchial tubes to the lungs (2) The oxygen is moved into the bloodstream (3) Circulates through the body (4) The cells in the body exchange the oxygen with carbon dioxide (5) The bloodstream carries the carbon dioxide back to the lungs (6) The lungs expel the carbon dioxide through the nose and mouth.  
Where does the following step fit into the given list of steps: A person breathes in oxygen 
Output (English):  Before step 1.