The Wavelengths Corresponding to the Harmonics of an Organ Pipe

The wavelengths corresponding to the harmonics of an organ pipe that is open at one end and closed at the other can be found by saying that the length of the pipe must be equal to

A) an odd number of quarter-wavelengths.
B) an odd number of third-wavelengths.
C) an odd number of half-wavelengths.
D) an integer number of half-wavelengths.
E) an integer number of wavelengths.