When two progressive sound waves travel in opposite directions and combine by superposition to produce a stationary wave, which statement correctly describes an antinode in this stationary wave?
- Aa position where the phase difference between the two waves is always $0^{\circ}$
- Ba position where the phase difference between the two waves is always $180^{\circ}$
- Ca position where the stationary wave has maximum amplitude
- Da position where the stationary wave has minimum amplitude