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 columnis close to the wave length 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 wave length of sound in air