Fact 1: Aging is associated with the death of cells.

Fact 2: Apoptosis means cell death.

Given the two facts above, answer the question "What is a natural part of aging?" with the following options: 
- Smoking
 - apoptosis
 - regeneration
 - illness
 - stimulation
 - cracking
 - Weight
 - firm skin


 

  apoptosis       