Which of the following securities is exempt from registration under the Securities Act of 1933?
a. a class of stock given in exchange for another class by the issuer to its existing shareholders without the issuer's paying a commission
b. limited partnership interests sold for the purpose of acquiring funds to invest in bonds issued by the US
c. corporate debentures that were previously subject to an effective registration statement, provided they are convertible into shares of common stock
d. shares of nonvoting common stock, provided their par value is less than $1.00
e. none of the above