Which of these actions is an example of erosion caused by gravity?
A.
​​​​Constant freezing and thawing water forming a hole in an asphalt road​​​​​

B.
​​​​​​Pieces of rock breaking off and falling from a mountain top

C.
​​​​​​​Chemicals in the air dissolve minerals in a marble statue​​​​​​​

D.
Plant roots widening cracks in a large granite rock