Independent variable definition: a variable (often denoted by x ) whose variation does not depend on that of another.
dependent variable definition: a variable (often denoted by y ) whose value depends on that of another.
controlled variable definition: control variable (or scientific constant) in scientific experimentation is an experimental element which is constant and unchanged throughout the course of the investigation. ... The control variables themselves are not of primary interest to the experimenter.
I believe the DBQ essay is the correct answer because "DBQ" means "document-based question," and it typically uses primary sources, so it would seem logical for that to be the answer.