A student measures water flow time through holes of different sizes. What is the hole size?

Correct answer: Independent variable

The direct answer is B, the independent variable. The independent variable is the factor deliberately changed by the experimenter. Here the student uses holes of different sizes, so hole size is the chosen input. The time taken for water to flow is the measured response and would be the dependent variable. Step by step: select hole size; keep other conditions such as water volume and container comparable; measure flow time; compare times; therefore hole size is independent. A is wrong because dependent variable is the measured effect, not the changed hole size. B is correct because size is deliberately varied. C is wrong because a controlled variable is kept the same, whereas hole size is not the same. D is wrong because “result” describes an outcome such as flow time, not the factor being changed. The question asks for the role of hole size, so classify the input rather than the measurement. Exam cue: “different sizes,” “different temperatures,” or “different concentrations” often identify the independent variable.