Final answer:
The correct option is 'd' as it directly assesses the long-term effectiveness and success of the company's strategy by evaluating sustainable competitive advantage and company performance.
Step-by-step explanation:
The question asking which of the following tests the merits of the firm's strategy and distinguishes it as a winning strategy is 'd. Is the strategy helping the company achieve a sustainable competitive advantage and is it resulting in better company performance?' A winning strategy would be one that not only supports the ongoing success of the company but also outperforms competitors in a sustainable way. Assessing whether a strategy is ethical, socially responsible, or balances well with growth and profitability (options a and b) are important considerations, but they do not directly assess the strategy's potential for securing long-term success. Option c, regarding the development of additional competitive capabilities, is part of creating a sustainable competitive advantage, but on its own does not fully assess the strategy's overall effectiveness in outperforming competitors. Option d is a more comprehensive assessment because it looks at both competitive advantage and overall performance results.