The figures $(A-D)$ show four animals. Select the correct option with respect to a common characteristic of two of these animals.

• A
  $(A)$ and $(D)$ respire mainly through body wall.
• B
  $(B)$ and $(C)$ show radial symmetry.
• C
  $(A)$ and $(B)$ have cnidoblasts for self-defence.
• D
  $(C)$ and $(D)$ have a true coelom.