The historical-return approach differs from the Gordon growth model because it is based primarily on past stock performance rather than on expected future dividends and growth. Under the historical-return method, analysts estimate the cost of common equity by examining the returns investors earned on the firm's stock over prior periods. The Gordon growth model, by contrast, is a forward-looking dividend-based approach that estimates the cost of equity as the expected dividend yield plus the constant growth rate of dividends. Choice D is correct because it captures the defining feature of the historical-return method. Choice B and choice C describe the Gordon growth model rather than the historical-return approach. Choice A is more closely associated with CAPM, which uses market risk and beta. Financial management often uses multiple methods to estimate the cost of equity because each approach has limitations. Historical returns can be useful as a reference point, but they may not reflect current risk or investor expectations. The Gordon growth model can be useful for stable dividend-paying firms, but it is less suitable for firms without predictable dividends. Therefore, D correctly explains the main difference between these two valuation methods.

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