Answer:
a. storage.
Explanation:
Storage is what allows a person keep what has been learnt in a memory. The seat of memory is called storage while the act of recalling the information stored in a storage location is called retrieval.
Given that Shayla is able to retain the vocabulary she learned in her first semester of Spanish class even though the class has ended. The main memory process that accounts for the fact that Shayla can hold information in her memory for extended periods of time is storage.