Which of the following animals share a common characteristic?$(a)$ $\text{Hydra}$, $(b)$ $\text{Fasciola}$, $(c)$ $\text{Pheretima}$, $(d)$ $\text{Asterias}$

1. A
   $(a)$ and $(d)$ have cnidoblasts for self-defence.
2. B
   $(c)$ and $(d)$ have a true coelom.
3. C
   $(a)$ and $(d)$ respire mainly through body wall.
4. D
   $(b)$ and $(c)$ show radial symmetry.