What is the correct way to identify variables in an experiment?

Correct answer: What was changed what was measured and what was kept the same

The answer is A. To identify variables, first ask three simple questions: what did the experimenter change, what did the experimenter measure, and what was kept the same? The changed factor is the independent variable, the measured result is the dependent variable, and unchanged conditions are controlled variables. A states exactly this complete method, so it is correct. B, which colour is beautiful, is a personal opinion and has no experimental role. C, which result is preferred, describes a preference rather than a variable and can introduce bias. D, which instrument is new, concerns equipment age, not the three scientific roles; a new instrument could be controlled, independent, or irrelevant depending on the design. Memory cue: change, measure, keep same = independent, dependent, controlled.