Megan volunteered to with a local political campaign and was assigned to stuff envelopes. she moved slowly at first but over time she became very efficient in her task. this is an example of a

Procedural memory

Explanation:

Procedural memory is referred to as a type of unconscious memory also known as the implicit memory and long term memory that tends to help the performance of a typical types of task without any conscious awareness of the previous knowledge.  This memory also tends to guide the processes that one tends to perform and also usually resides below state of the conscious awareness.

the correct answer is c.