Fact 1: Cycles of freezing and thawing water cause ice wedging.

Fact 2: Water is made up of H2O molecules.

Given the two facts above, answer the question "what freezes and thaws to cause ice wedging?" with the following options: 
- h2o
 - dams
 - oxygen
 - clouds
 - carbon
 - rain
 - lake
 - H20


 

 h2o        