Item CV023005: In an experiment involving two variables (X and Y) that could affect the outcome of the experiment, changing X and keeping Y constant allows you to find out the effect of X on the outcome of the experiment.
A student thinks that there are two variables (X and Y) that may affect the result of her experiment. She decides to change only variable X and let variable Y stay the same. What can the student find out about the effects of variables X and Y?

Distribution of Responses Percent of students responding correctly
 