Refer to the Diagram Below

Refer to the diagram below. What is the correct order of structures in the electrical excitation pathway that generates a normal heartbeat?

A) 2, 5, 1, 4, 6, 3
B) 3, 6, 2, 4, 1, 5
C) 1, 5, 4, 2, 3, 6
D) 1, 2, 3, 4, 5, 6
E) 3, 2, 6, 4, 5, 1
F) 6, 3, 2, 4, 5, 1