The test site of this topic is the structural characteristics and classification of cardiac glycosides. The side chain of cardiac glycoside C- 17 is a five-membered unsaturated lactone ring, also known as cardiotonic. The C- 17 side chain of cardiac glycoside b is a six-membered unsaturated lactone ring, also known as styrene or bufotoxin. Option A: Bufo steradiene belongs to cardiac glycoside B, and deacetyl cornucopia belongs to cardiac glycoside A, which consists of aglycone, three D- digitalis toxins and one glucose. Option b belongs to flavonoids, option c belongs to steroidal saponins, and option d belongs to triterpenoid saponins.