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

Fact 2: Ice is frozen water.

Given the two facts above, answer the question "What causes ice to expand as it is formed?" with the following options: 
- precipitation
 - water
 - Physical weathering
 - sunlight
 - music
 - Condensation
 - heat produced
 - hydrogen bonds


 

        hydrogen bonds 