I believe the answer is: ability to solve geometry problems
Dependent variables refers to the type of variable that can be influenced by other variables in the research. In the eample above, ability to solve geomatry problems could be influenced by the type of meals that the subject had (which is a part of control variables)
Dr. Martinez is studying the effects of diet on mental alertness. each morning for two weeks, subjects in Dr. Martinez's study eat a breakfast that is either high in carbohydrates or high in protein. Dr. Martinez then measures the subjects' abilities at solving geometry problems. The dependent variable in this study is the ability to solve geometry problems.
