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

Fact 2: Water is made up of H2O molecules.

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


 

        h2o 