Final answer:
In a residual plot against x that does NOT suggest we should challenge the assumptions of our regression model, we would expect to see a c. horizontal band of points centered near 0.
Step-by-step explanation:
In the context of regression analysis, a residual plot helps us assess the fit of a regression model. When analyzing a residual plot against the independent variable x, a pattern that does NOT suggest we should challenge our model's assumptions would be a c. horizontal band of points centered near 0. This indicates that the residuals are evenly spread around the regression line and do not show a systematic pattern. Such a distribution of points supports the idea that the regression line fits the data well, the error variance is constant (homoscedasticity), and the model assumptions are likely to be valid.
If we observe a parabolic or widening band of points, or a band with a slope, it would indicate that the assumptions of equal variance, linearity, and independence of errors might be violated.