You are presented with the question "what causes brain atrophy?" and the following answer choices: 
- Smoking
 - sodium
 - Dehydration
 - sweating
 - death
 - birth
 - Veins and arteries.
 - lack of oxygen

Now knowing that brain cells die quickly if their oxygen supply is cut off and brain atrophy means the brain matter has shrunk, often because brain cells are dying or dead, choose the best answer.


 

        lack of oxygen 