The Fama and French evidence that high book-to-market firms outperform low book-to-market firms even after adjusting for beta means that _________. A) high book-to-market firms are underpriced or the book-to-market ratio is a proxy for a unique risk factor B) low book-to-market firms are underpriced or the book-to-market ratio is a proxy for a systematic risk factor C) either high book-to-market firms are underpriced or the book-to-market ratio is a proxy for a systematic risk factor D) high book-to-market firms have more post-earnings drift