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. Given these facts, what causes brain atrophy among the following options:
- Smoking
 - sodium
 - Dehydration
 - sweating
 - death
 - birth
 - Veins and arteries.
 - lack of oxygen


 

        lack of oxygen 