Choice "C" is correct. An official bond is a type of surety bond. Many states require public officials to obtain bonds from a surety for faithful performance of their duties. Such bonds obligate a surety for all losses that the public official causes by negligence or nonperformance of required duties.
Choice "b" is incorrect. A convertible bond is a corporate bond that may be converted into stock. A convertible bond has nothing to do with the obligations of a surety.
Choice "a" is incorrect. A debenture bond is simply an unsecured corporate bond. A debenture bond has nothing to do with the obligations of a surety.
Choice "d" is incorrect. A municipal bond is a bond issued by a city or other local government. A municipal bond has nothing to do with the obligations of a surety.