Astudent measures the range of sound frequencies that the human ear can hear by playing sounds for volunteers between 10 and 30,000 hertz and asking them to raise their hand if they were able to hear it. what type of variable is the independent variable in this experiment?

The independent variable is the sound variable. This is because the independent variables, in this case the sound frequencies, is the ones that is controlled/varied to test its effects on the capacity of the volunteers to perceive the sound. Therefore the volunteers (and their ability to perceive the different sound frequencies) are the dependent variable.

i think the answer is b.