9.
which describes the variable that is changed to test the prediction?

Independent variable is the one that can be changed to test the prediction.

Explanation:

In order to test the prediction in an experiment, the independent variables are always changed.  This is because the independent variable are the one that is always produces different cause and effect in an experiment.

They are not dependent on the outcome of the experiment but can alter the experiment to any extend when they are altered.  Hence we can conclude independent variable as right answer.

"do a testcross with a homozygous recessive plant."