Final answer:
Convertible preferred stock can be exchanged for common stock at a constant ratio, unlike treasury stock, callable preferred stock, or participating preferred stock. Hence, option (c) is correct.
Step-by-step explanation:
The option that can be exchanged for common stock at a constant ratio is convertible preferred stock. Convertible preferred stock is a type of preferred share that gives the holder the right to convert their shares into a predetermined number of common shares after a specified date. This conversion can usually be done at any time at the discretion of the shareholder, and the ratio at which the preferred shares are converted to common shares is fixed at the time of issuance of the convertible preferred stock.
Treasury stock, callable preferred stock, and participating preferred stock do not generally have a provision that allows for conversion into common stock. Treasury stock refers to shares that were once in circulation but have been bought back by the issuing company. Callable preferred stock gives the issuing company the right to repurchase the stock at a set price after a certain date. Participating in preferred stock often allows for dividend payments that exceed the common dividend rate and may participate in additional earnings.