Retention is how the brain encodes information.

Retention is indeed how the brain encodes informaiton. Or rather, it could be said that retention is a way how the brain remembers things and enables us to recall them at a later stage in life. This isn't the case with people who have some sort of memory lesions. 

Well i had the same answer, so the correct answer would be a. but in this case it would be the one with plasma membrane and cell wall circled that is next to the hairy pill type of thing.