You are presented with the question "What can cut off the oxygen to cells?" and the following answer choices: 
- Sulfur dioxide
 - oxygen atoms
 - the heart stopping
 - massive damage
 - smoking pipes
 - water
 - hair
 - cigarettes

Now knowing that brain cells die quickly if their oxygen supply is cut off and brain cells begin to die as soon as the heart stops pumping oxygen, choose the best answer.


 

   the heart stopping      