Fact 1: Ice wedging is when ice causes rocks to crack by expanding in openings.

Fact 2: Ice wedging is the most important form of mechanical weathering.

Given the two facts above, answer the question "What is a form of mechanical weathering?" with the following options: 
- microbes breaking down rock
 - By coral exoskeletons
 - wind and erosion
 - oxygen breaking down rock
 - ice expanding in rock openings
 - removal of rock by acid rain
 - remains of prehistoric life
 - fissures of hot, acidic water


 

     ice expanding in rock openings    