Fact 1: Weathering means breaking down rocks from larger whole into smaller pieces by weather.

Fact 2: Water is a mechanical weathering force.

Given the two facts above, answer the question "What breaks rocks down?" with the following options: 
- In the winter
 - Calcium carbonate
 - an engine
 - the Great Barrier Reef
 - mechanical force
 - permineralization
 - at or near the margins
 - mechanical


 

     mechanical force    