The response variable in a study refers to the outcome or dependent variable, which is what you're trying to predict or explain. In this case, the researcher is attempting to estimate the volume of usable lumber based on the height of the tree. Therefore, the response variable is the volume.

The predictor or explanatory variable is the height, as it is being used to estimate the volume.

Thus, the correct answer is: A. Volume

Would you like further details on this or have any additional questions?

Here are 5 related questions to deepen your understanding:

1. What is the predictor variable in this scenario?
2. How can a regression model help in predicting the volume based on the height?
3. What are some methods to evaluate the accuracy of the regression model in this case?
4. How would you describe the relationship between height and volume based on the scatter plot?
5. Could the relationship between height and volume be non-linear? How would you check this?

Tip: Always ensure to label your response and predictor variables correctly when setting up any regression analysis.