Johanna was asked to remember a string of letters. She heard $x$ during the presentation of the letters. In her brain, this input was changed into the neural code $s$ Later, when she was asked to recall the letters, Johanna included $s,$ not $x,$ in her list. Johanna most likely made this error on the recall test due to an error in the __________.
phase of memory.
a) encoding
b) retrieval
c) acquisition
d) storage