What Does George Miller Mean by the "Magic Number Seven

What does George Miller mean by the "Magic Number Seven plus or minus two"?

A) The number of pieces of information the average person can easily recall after a single exposure.
B) The amount of information that can be memorized in one sitting.
C) The number of saccadic eye movements in a fixation.
D) The time it takes information to pass from short-term memory to long-term memory.