Along a straight line, points A, B, C, D and E are marked such that AB = BC = CD = DE = 4cm. At a particular instant of a transverse wave snapshot:
• Point B is at maximum upward displacement.
• Point D is at maximum downward displacement.
• Points A and C cross the mean position moving upward.
• Point E crosses the mean position moving downward.
Which of the following distances equals one complete wavelength of the wave?
(a) AB
(b) BD
(c) AE
(d) AD