A researcher is studying the effects of memory training games on subsequent IQ test performance. One group plays the memory games while the other group does nothing. Both groups take an IQ test. The researcher also notes that one group, on average, completed more years of formal schooling than the other. In this case, years of formal schooling is best described as a(n):
A. Extraneous variable.
B. Dependent variable.
C. Independent variable.
D. Interacting variable.
