Diploblastic animals occur in
A. Annelida
B. Porifera
C. Coelenterata
D. Both (B) and (C)

Hint: Animals develop their tissues, organs, and organ system from the cells that form the three embryonic layers, and based on the number of these embryonic layers animals are classified into either diploblastic or diploblastic organisms.

Complete answer:
In diploblastic organisms, the cells form the two embryonic layers that are outer layer ectoderm and an inner layer endoderm. Diploblastic organisms do not develop true organs because of the absence of mesoderm. These animals have such a blastula that involves Ctenophora and Cnidaria.
A. Annelida- Phylum Annelida is bilaterally symmetrical, triploblastic organisms i.e. in these organisms cells form three embryonic layers that are ectoderm, endoderm, and mesoderm. They are an example of coelomate i.e. coelom is present which is a cavity between the body wall and the gut wall which is lined by mesoderm. This phylum includes worms.
B. Porifera- Phylum Porifera is an exclusive classification of aquatic animals including the sponge-like structure and is multicellular organisms. They are also known as sponges i.e. pore-bearing animals. Porifera are also diploblastic as they have cells arranged in two embryonic layers i.e. endoderm and ectoderm.
C. Coelenterata- Phylum Coelenterata is a group of aquatic and marine organisms with a radially symmetrical body. They are diploblastic organisms in which the body is made up of two embryonic layers i.e. ectoderm (lining the outside the body), and endoderm (inner lining of the body).

Hence, the correct answer is option (D).

Note: Animals in phylum Coelenterata have no coelom and they have only a single opening in the body. They contain sensory tentacles which are formed from nematocysts for prey capture. Animals in phylum Porifera are multicellular that have bodies full of pores and channels which allows water to circulate.