A study is conducted of standardized test scores between two school districts. In the​ study, a confounding variable was suspected to be family income. After a multiple regression was performed with variables​ DISTRICT, INCOME, and DISTRICT times ×​INCOME, a model was adopted. When this model is restricted to each of the​ districts, the resulting lines are parallel. What can we conclude about the results of the multiple​ regression?
A. The interaction between the district and income level was found to be statistically significant.
B. The contribution of the variable DISTRICT is not statistically significant.
C. The interaction between the district and income level was found not to be statistically significant.
D. The mean scores for each district are roughly identical.