S.D / steroids are naturally occurring or synthetic fat-soluble tetracyclic compounds. Which contains four rings. Ring A=Cyclohexane ring Ring B=Cyclohexane ring Ring C=Cyclohexane ring Ring D=Cyclopentane ring (Basic Steroidal Nucleus) The groups which are shown by thick line (---) are above the plane of the nucleus & denoted by (B) The groups which are shown by the dotted line (….) are below the plane. Of the nucleus & are denoted by (Alpha).