A wave disturbance traveling in and enters a medium in which its velocity is less than that in air. Which of the following statements is true about the wave in the medium?
A. both the frequency of the wave and the wavelength and decreased B. the frequency of the wave is deceased while the wavelength is increased C. the frequency of the wave in unaltered while the wavelength decreased D. the frequency of the wave is decreased while the wavelength is unaltered
