Four Traveling Waves Are Described by the Following Equations,where All

Multiple Choice

Four traveling waves are described by the following equations,where all quantities are measured in SI units and y represents the displacement. I: y = 0.12 cos(3x + 2t)
II: y = 0.15 sin(6x - 3t)
III: y = 0.23 cos(3x + 6t)
IV: y = -0.29 sin(1.5x - t)
Which of these waves have the same speed?

A) I and III
B) I and IV
C) II and III
D) I and II
E) III and IV