A student performed the experiment to measure the speed of sound in air using resonance air-column method. Two resonances in the air-column were obtained by lowering the water level. The resonance with the shorter air-column is the first resonance and that with the longer air-column is the second resonance. Then,
A. the intensity of the sound heard at the first resonance was more than that at the second resonance
B. the prongs of the tuning fork wer kept in a horizontal plane above the resonance tube
C. the amplitude of vibration of the ends of the prongs is typically around 1 cm
D. the length of the air-column at the first resonance was somewhat shorter than 1/4th of the wavelength of the sound in air
