In the experiment to determine the speed of sound using a resonance column, (A) prongs of the tuning fork are kept in a vertical plane (B) prongs of the tuning fork are kept in a horizontal plane (C) in one of the two resonances observed, the length of the resonating air column is close to the wavelength of sound in air (D) in one of the two resonances observed, the length of the resonating air column is close to half of the wavelength of sound in air