Answer: The type of material used to make the club head.
Step-by-step explanation:
The independent and dependent variables are the central factors in an experiment. The independent variable is the one that is controlled, as it is modified on purpose to examine the consequences on the dependent variable, which is the one being measured through the scientific experiment.
In this example, the type of material used to make the clubhead is the independent variable and the distance she hits the golf balls is the dependent variable.