Potential Remedies for When Your Model Suffers from the Endogeneity

Multiple Choice

Potential remedies for when your model suffers from the endogeneity problem include all of the following except what?

A) Gather (additional) data on a possible instrumental variable.
B) Gather (additional) longitudinal data to allow for a fixed effect approach.
C) Gather (additional) control variables that would limit the endogeneity concern.
D) Check if the residuals from your regression are uncorrelated with your treatment.