A control variable is a value which may affect the outcome and therefore must be kept constant or monitored.

• A. The independent variable.
• B. The dependent variable.
• C. A value which may affect the outcome and therefore must be kept constant or monitored.
• D. The experimental outcome.

Answer: (C)

A control variable is a factor that could influence the result, so it is kept the same or watched carefully to prevent it from swaying the outcome. This lets you see what happens when you change only the factor you’re interested in testing. In this question, the statement that describes that idea exactly is the one that says a value which may affect the outcome and therefore must be kept constant or monitored. The independent variable is what you deliberately change, the dependent variable is what you measure, and the experimental outcome is the result you observe, not a factor you hold constant. For example, when comparing how different light levels affect plant growth, you’d vary light (independent variable) and measure growth (dependent variable) while keeping factors like water, soil, and pot size as control variables so they don’t affect the comparison.