Indicate the answer choice that best completes the statement or answers the question.

$$ Which of the following statements is CORRECT?

a$.$ The preferred stock of a firm carries a similar level of risk to that of the firm's common stock.

b$.$ The common stock of a given firm is safer than the preferred stock of a same firm.

c$.$ Corporations cannot buy the preferred stocks of other corporations.

d$.$ The preferred stock of a firm carries a similar level of risk to that of the firm's bonds.

e$.$ The preferred stock of a given firm is generally more risky to investors than the bond of a same firm.