Given a list of steps and an additional step, determine where the step fits into the original list of steps. A correct answer, correctly places the given step into the set of steps so that it creates a new plausible set of steps. Output must be formatted as 'After step n', where n is the step number after which the given additional step is to be inserted.

Let me give you an example: Steps: (1) Solar radiation reaches Earth's atmosphere (2) Some is reflected back into space (3) The rest of the energy is absorbed by land and oceans, heating the Earth (4) Some of this heat is trapped by greenhouse gases in the atmosphere (5) Human activities such as burning fuel are increasing the amount of greenhouses gases (6) This causes more heat radiation to stay trapped in our atmosphere (7) The Earth's temperature rises  
Where does the following step fit into the given list of steps: Heat radiates from Earth to space 
The answer to this example can be:  After step 3. 
Here is why: The correct answer is 'After step 3'. The given step is 'Heat radiates from Earth to Space'. Step 3 introduces a new concept of generated heat. Step 4 mentions that the heat is trapped into the atmosphere. In order for the heat to get to the atmosphere, the heat must radiate from Earth to space. Therefore, the correct answer is 'After step 3.'

OK. solve this:
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 
Answer:
 Before step 1. 