The following described securities are legal investments:
(a) Obligations in the form of bonds and notes issued, assumed, or guaranteed by entities incorporated in the United States of America. The obligations shall be among the 3 highest ratings of any NRSRO. Convertible bonds of a lesser rating will be legal if the common stock would otherwise qualify.
(b) All preferred stocks issued, assumed or guaranteed by entities incorporated in the United States. The obligations shall be rated among the 3 highest ratings of any NRSRO.
(c) The common stock or senior securities convertible into common stock of entities incorporated in the United States of America provided:
(1) The stock is listed on an exchange and is ranked among the 3 highest ratings of any NRSRO.