In a controlled science experiment, which variables must you keep the same to ensure a fair test?

• A. The independent variable
• B. The dependent variable
• C. The measurement tool
• D. The control variables (constant variables) must be kept the same.

Answer: (D)

When you want to know if something you change really caused a difference, you keep all the other factors the same. That way, any change you observe in the outcome is likely due to the factor you’re testing, not something else. Those factors you hold steady are the control variables.

So, the best choice is to keep the control variables constant—things like temperature, light, amount of water, or the material being tested. If those change, they could influence the results, making it unclear whether the Independent Variable is really responsible.

The independent variable is the one you deliberately change to see its effect, so it isn’t kept the same. The dependent variable is what you measure, and it will vary because of that change, so it isn’t kept the same either. Using the same measurement tool helps keep measurements consistent, but the key idea for a fair test is keeping all other potential factors constant as control variables.