Dividend yield is most often computed for common stock because

a$.$ the cash dividends paid on common stock normally vary with the profitability of the corporation.

b$.$ the preferred stock market price per share is always lower than common stock, causing an inflated dividend yield.

c$.$ common stock dividends are always lower than preferred stock dividends and present the most conservative estimates of dividend yield.

d$.$ the preferred stock dividends vary with the profitability of the corporation.