If ice causing rocks to crack by expanding in openings is a form of mechanical weathering, then what is a form of mechanical weathering?

Answer choices:
- 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     