State reasons for the following:
$(a)$ Mammals have mammary glands.
$(b)$ Annelids have a true body cavity.
$(c)$ Fish possess gills.

(N/A) Mammals have mammary glands to produce milk for nourishing their young ones.
$(b)$ Annelids have a true body cavity (coelom) because they exhibit a high degree of organ differentiation and tissue organization,allowing for complex internal systems.
$(c)$ Fish possess gills to extract dissolved oxygen from water,which is essential for their respiration in an aquatic environment.