Question $1(1$ point$)$

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Four waves are described by the following expressions, where distances are measured in meters and times in seconds.

I $y=0\mathrm{.}12cos(3x-21t)$

II $y=0\mathrm{.}15sin(6x+42t)$

III $y=0\mathrm{.}13cos(6x+21t)$

IV $y=-0\mathrm{.}23sin(3x-42t)$

Which of these waves have the same speed?

II and IV

II and III

I and III

III and IV

I and II