The characteristics of Class $Reptilia$ are:

• A
  Body covered with moist skin which is devoid of scales,the ear is represented by a tympanum,alimentary canal,urinary and reproductive tracts open into a common cloaca.
• B
  Fresh water animals with bony endoskeleton,air-bladder to regulate buoyancy.
• C
  Marine animals with cartilaginous endoskeleton,body covered with placoid scales.
• D
  Body covered with dry and cornified skin,scales over the body are epidermal,they do not have external ears.