Explain which biotic factors used by the beaver are related to its role as a keystone species

A keystone species refers to a species on which other organisms in an ecosystem are largely reliant on, like that if they are withdrawn, the ecosystem would change radically.  

The prime biotic factors used by a beaver are trees. The beavers utilize trees to construct a dam to obstruct the movement of water that in turn modifies the influence of the abiotic factor water on the surrounding.  

c. movement because i took the test and it lets me review my answers