Answer:
c. The reasoning of both Alfons and Mary suffers from the omitted variable problem
Step-by-step explanation:
The issue of omitted variables occurs as a result of mis-specification of a linear regression model, which could be either because the impact of the omitted variable on both the dependent variable is unclear, or the evidence was not accessible.
This causes you to omit the variable from your regression, resulting in over-estimation (upward bias) or underestimation (downward) of the influence of one of the other predictor variables.