The correct option is C Gastrula
Most animals reproduce sexually, and the diploid stage usually dominates the life cycle. In most species, a small, flagellated sperm fertilizes a larger, non-motile egg, forming a diploid zygote. The zygote then undergoes cleavage, a succession of mitotic cell divisions without cell growth between division cycles. During the development of most animals, cleavage leads to the formation of a multicellular stage called a blastula, which in many animals takes the form of a hollow ball. Following the blastula stage is the process of gastrulation, during which layers of embryonic tissues that will develop into adult body parts are produced. Thus, the cells of various layers get differentiated and get destined to form different organs of the animal body. The resulting developmental stage is called as gastrula.