In wave diffraction, which two factors primarily determine how much a wave spreads after passing through an opening (or around an obstacle)?

• A. The medium’s density and the wave’s phase at the opening
• B. The wave’s amplitude and the distance the wave travels after the opening
• C. The wavelength of the wave and the size (width) of the opening/obstacle relative to that wavelength
• D. The wave’s frequency and its polarization direction

Answer: (C)