Firstly, let's understand what a dependent variable is. A dependent variable is what we measure in the study and what is affected during the experiment. It's the variable that represents the outcome or result we are interested in.
In this particular scenario, we are interested in the outcomes from three different types of math instruction: a computer-assisted class, a videotaped course, or a regular classroom. Additionally, we are taking into account a second independent variable, the student's sex.
However, what we aim to measure isn't any of those factors (type of math instruction or sex), but the students' performance on a standardized math achievement test. Thus, our dependent variable is the one we're seeking to measure and that might be affected by the independent variables (type of math instruction and the subject's sex).
So, the correct answer is D. The scores on the math achievement test would be regarded as the dependent variable in this study.