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 "What causes H20 to expand when frozen?" with the following options: 
- evaporation
 - vaporization
 - hydrogen bonds
 - helium bonds
 - mysterious forces
 - nitrogen bonds
 - Physical weathering
 - precipitation


 

   hydrogen bonds      