The Information Ratio (IR) is the most appropriate metric for evaluating a manager's ability to generate alpha through active management. It measures the excess return generated relative to the benchmark per unit of tracking error, which reflects both stock-picking and market-timing skills. Since Manager A has the highest IR, they are the best at generating consistent alpha through active decisions.

B is incorrect: Manager B has the lowest tracking error, which indicates minimal deviation from the benchmark. While this might suggest disciplined or conservative management, it does not reflect strong active management skills. Low tracking error is more characteristic of passive or benchmark-hugging strategies rather than skillful active management.

C is incorrect: The Sharpe Ratio measures the risk-adjusted return of a portfolio relative to the risk-free rate, not the benchmark. While Manager C has the highest Sharpe Ratio, this reflects their ability to manage total portfolio risk and generate absolute returns, not their ability to outperform the benchmark through active management. Therefore, this metric is not relevant for evaluating active management skills.

D is incorrect: Manager D has the highest tracking error, which indicates significant deviation from the benchmark. However, high tracking error alone does not imply skillful active management. Without a correspondingly high Information Ratio, the deviations could be due to poor decisions or excessive risk-taking rather than alpha generation. Thus, Manager D’s high tracking error does not necessarily indicate superior active management skills.