Final answer:
In the experiment regarding the effect of music on test scores, the test scores themselves represent the (d) dependent variable, as they are the outcome being measured in response to the manipulated independent variable, which is the music.
Step-by-step explanation:
In the experiment to investigate whether playing music while taking a test affected students' test scores, the test scores would be the dependent variable. This is because the dependent variable is what researchers measure to determine the effects of changes in the independent variable, which in this case would be the presence or absence of music during the test.
The independent variable is the one manipulated by the experimenter to observe effects on the dependent variable. Students' test scores change as a result of the experimental manipulation, which is why they are referred to as dependent variables.