An independent variable is one that

A) is irrelevant to what happens in the experiment.
B) the experimenter cannot control or measure.
C) the experimenter changes or controls..
D) the experimenter measures after the treatment.

An independent variable is the variable that the experimenter changes or controls in order to observe its effect on the dependent variable. It is a variable that is intentionally manipulated in an experiment. Option A and D are incorrect as the independent variable is not irrelevant or measured after the treatment, and option B is incorrect as the experimenter should be able to control or manipulate the independent variable.