How does the Doppler effect explain why a siren's pitch increases as it approaches you? A. The siren moves away from sound waves it has already produced, increasing their wavelength. B. The siren moves closer to sound waves it has already produced) decreasing their wavelength C. The siren moves away from sound waves it has already produced decreasing their wavelength, D. The siren moves closer to sound waves it has already produced, increasing their wavelength