A forester wishes to predict the volume (in cubic feet) of usable lumber in a certain species of tree using the height (in feet) and diameter (in inches) of the trees. The height and diameter of 31 trees of a certain species were measured, the trees were cut down, and the volume of usable lumber was determined. The response and explanatory variable(s) in this study are:

The explanatory variable is a type of independent variable manipulated by the experimenter for the ongoing experimental study.
The response variable is a type of dependent variable which depends on the explanatory values provided by the experimenter.

Given: A forester wishes to predict the volume (in cubic feet) of usable lumber in a certain species of tree using the height (in feet) and diameter (in inches) of the trees.

Here, Volume directly depends upon the height and diameter of the tree.

Also, forester ( Experimenter) wants to predict volume by cutting tree that means it is an response variable and it depends on height and diameter , so height and diameter are explanatory variable.

Hence, The response variable = Volume

and explanatory variable(s) in this study are: Height and Diameter.