All of the Following Are True, with the Exception of One

Short Answer

All of the following are true, with the exception of one condition: a. a high $R ^ { 2 }$ or $\bar { R } ^ { 2 }$ does not mean that the regressors are a true cause of the dependent variable.
b. a high $R ^ { 2 }$ or $\bar { R } ^ { 2 }$ does not mean that there is no omitted variable bias.
c. a high $R ^ { 2 }$ or $\bar { R } ^ { 2 }$ always means that an added variable is statistically significant.
d. a high $R ^ { 2 }$ or $\bar { R } ^ { 2 }$ does not necessarily mean that you have the most appropriate set of regressors.