The is responsible for determining the frequency of vibration of the air column in the tube within a wind instrument. a. effective length of the tube b. type of reed used c. reed's frequency of vibration d. humidity of the air

The answer is A. effective length of the tube
In wind instrument, the effective length is not the actual length of the instrument but only the length that the finger holes manage to cover.
The more holes it managed to cover, the higher frequency of vibration it might able to produce, which lead to higher pitch of the instrument.