Final answer:
In Christian's study, the independent variable is the time spent studying, the dependent variable is test performance, and controlled variables are other factors that could influence test performance.
Step-by-step explanation:
In Christian's survey of class members to determine how the time spent studying affects test performance, the independent variable is the amount of time a student spends studying. This is because it is the variable that Christian is manipulating to observe its effects on the other variable. On the other hand, the dependent variable is the performance on the test, as this is expected to change in response to the amount of studying done. Lastly, controlled variables would be any other factors that could influence test performance (such as difficulty of the material or test-taking skills) that Christian keeps constant in order to ensure that the changes in the dependent variable are solely attributable to the independent variable.