What Was Psychologist George Miller Describing in His Paper Entitled

What was psychologist George Miller describing in his paper entitled "The Magical Number Seven, Plus or Minus Two"?

A) the average duration of echoic memory in seconds
B) the duration in years before most of the current information in long-term memory is forgotten
C) the number of trials it takes a typical student to memorize a list of 13 nonsense syllables
D) the number of items or bits of information that can be held in short-term memory at one time