The blank represents the input of a relation.
F Constant
G Range
H Independent Variable
J Dependent Variable

The correct answer is H. Independent variable.

Step-by-step explanation:

The independent variable, typically represented with the variable x, is the input of the function.  In an experiment, this is the variable that the scientist changes in order to see a change in the dependent variable.  The independent variable is usually plotted along the x-axis and its values represent the domain of the function.

The dependent variable, conversely, is typically represented with the variable y, and represents the output of the function.  In an experiment, the dependent variable would represent that change that occurs due to a change in the independent variable.  The dependent variable is usually plotted along the y-axis and its values represent the range of the function.

Hope this helps!