The electroencephalogram (EEG) below was recorded from a sleeping individual. It displays several distinct brain wave patterns, each indicated by a letter. Based on the defining visual characteristics of a rapid burst of higher-frequency waves, which letter points to the sleep spindle? [Image of an EEG with sections A, B, and C labeled. Section A points to a rapid burst of high-frequency waves. Section B points to a single large, high-amplitude wave. Section C points to the general low-frequency