Part 5: All of the following are true, with the exception of one condition: A) a high R2 or does not mean that the regressors are a true cause of the dependent variable. B) a high R2 or does not mean that there is no omitted variable bias. C) a high R2 or always means that an added variable is statistically significant. D) a high R2 or does not necessarily mean that you have the most appropriate set of regressors.