With this science question and explain if you can! i'm so confused

In this experiment, the independent variable is the surface, the dependant variable is the distance one end of the surface must be lifted to see movement of the object, and the control variable is the object. Since the surface height at one end is changed and the object is kept the same, the only conclusion that can be made is whether the surface has an effect on the force of friction. Of course, basic physics tells you that it does, therefore A is correct.