Fact 1: Hydrogen bonds cause water to expand when it freezes.

Fact 2: Water is everywhere H20.

Given the two facts above, answer the question "Hydrogen bonds cause what to expand when it freezes?" with the following options: 
- salt
 - mercury
 - NaCl
 - lake
 - H20
 - rain
 - h2o
 - oxygen


 

     H20    