Four traveling waves are described by the following equations, where all quantities are measured in SI units and y represents the displacement. 1: y = 0.12 cos(3x - 21t) Il: y = 0.15 sin(6x + 42t) Ill: y = 0.13 cos(6x + 21t) IV:y = -0.27 sin(3x - 42t) Which of these waves have the same period? O I and II, and also III and IV O I and IV, and also II and III O All of them have the same period. O They all have different periods. O I and Ill, and also II and IV