Answer:
noise would be the independent variable, or manipulated variable.
Step-by-step explanation:
The independent variable of an experiment is the thing that is changed throughout the experiment. So in the experiment with how noise affects tests, the noise level would change. The dependent variable, or responding variable, is the result of the independent variable. So, the dependent variable would be how well students did on their tests. The scientists have no direct control over it, the only thing they have direct control of is the independent variable, which is the noise level.
I hope this helps :)