Which of the following statements are correct concerning municipal bonds (muni's)? :I. Yields on muni's are usually lower than yields on Treasury bonds. :II. Muni's are more appealing to individuals with high incomes. :III. Interest on muni's is exempt from federal income tax. :IV. Muni's are less risky than Treasury bonds. a. II, III and IV only b. I, II, III and IV c. I, II and III only d. II and III only