Remembering how to ride your bike is an example of a .

Having the ability o remember how to ride a bike is an example of a long term memory.  This is procedural memory; knowing how to do something, having the skills and the formation of simple associations. These skills are able to be recalled at any time.

Procedural

Procedural memory helps people understand how stuff works. It is primarily involves in knowing new motor skills like learning how to ride a bike or play a piano. The brain begin building and assigning interneuron pathways for cerebellum and basal ganglia to outflow muscle information to the legs or hands developing motor coordination.

Moreover, procedural memory is part of the long-term memory that is responsible for storing information on how to perform certain procedures.

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

it is either c or d and i know for sure it is not a or b