You are presented with the question "what does hydrogen bonds cause to expand when it freezes?" and the following answer choices: 
- oxygen
 - atomic bombs
 - rain
 - NaCl
 - H20
 - lake
 - hydrogen
 - h2o

Now knowing that hydrogen bonds cause water to expand when it freezes and water is made up of H2O molecules, choose the best answer.


 

        h2o 