Fact 1: Increasing heat causes thermal expansion.

Fact 2: Thermal fatigue cracking is notably different than thermal expansion damage.

Given the two facts above, answer the question "what can cause fatigue?" with the following options: 
- cigarettes
 - Dehydration
 - expansion
 - Pollution
 - influenza
 - hormones
 - sweating
 - smoking


 

   expansion      