Answer:
c. gastrulation
Step-by-step explanation:
All the tissues and organs of an animal are formed from germ layers. There are two types of animals, diploblastic and triploblastic. Diploblastic organisms have two germ layers, ectoderm and endoderm. Triploblastic organisms have an additional layer, mesoderm. During the process of gastrulation, blastula ( hollow ball of cells ) forms ectoderm and endoderm. These two layers interact with each other to form mesoderm.
Ectoderm forms mammary glands, skin, hair etc. Endoderm gives rise to inner lining of digestive tract, lungs and thyroid. Mesoderm forms bone, connective tissue, heart etc.