A simple linear regression model is constructed to see how well average American College Testing (ACT) scores in Chicago help predict college enrollment rate. Below, the residuals of the model are plotted against the fitted values. What does the figure imply to be wrong about the model?

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Residuals 20 0 -20 -40 8 00 8 00 40 80%0 O 89 0 0 2088 O O 60 8 00 00 00 abo 80 Fitted values 100 120 O O