As a Wave Moves to the Right in an Elastic

As a wave moves to the right in an elastic rope, a sequence of pictures 1 through 6) is taken at intervals of one second. There is a small particle attached to the rope, as shown in the figures. If the width of the figure is 8 cm, this wave has a period of

A) 0.2 s.
B) 10 s.
C) 3 s.
D) 6 s.
E) 12 s.