You are presented with the question "What causes H20 to expand when frozen?" and the following answer choices: 
- evaporation
 - vaporization
 - hydrogen bonds
 - helium bonds
 - mysterious forces
 - nitrogen bonds
 - Physical weathering
 - precipitation

Now knowing that hydrogen bonds cause water to expand when it freezes and water is everywhere H20, choose the best answer.


 

   hydrogen bonds      