The figure shows a sound wave as a function of time when the source is stationary with respect to the observer. An Illustration of a transverse wave and four crests and four troughs are labeled 1 s total. Which shows the perceived sound wave heard by a stationary observer when the source moves toward the observer? An illustration of a transverse wave and three crests and three troughs are labeled 1 s total. An Illustration of a transverse wave that is taller than the previous. Three crests and three troughs are labeled 1 s total. An Illustration of a transverse wave and four crests and four troughs are labeled 1 s total. An Illustration of a transverse wave and seven crests and seven troughs are labeled 1 s total. Mark this and return