What is a control in an experiment?

• A. The variable you purposely change.
• B. The data you collect during the experiment.
• C. A standard used for comparison, kept the same while testing the independent variable.
• D. An instrument used to measure results.

Answer: (C)

A control is the standard used for comparison, kept the same while testing the independent variable. It gives you a baseline so you can tell if the factor you changed actually caused any difference, or if results came from other factors.

For example, if you’re testing whether fertilizer helps plants grow, you’d have one group with fertilizer and another group without fertilizer, with all other conditions (water, soil, sunlight) kept the same. The group without fertilizer serves as the control because it shows how tall the plants grow under normal conditions. The other choices describe different parts of an experiment: the thing you deliberately change is the independent variable, the data are what you collect, and an instrument is a tool used to measure.