The correct option is B Gastrula
Gastrulation is a phase early in the embryonic development of most animals, during which the single-layered blastula is reorganized into a trilaminar ("three-layered") structure, known as the gastrula. These three germ layers are known as the ectoderm, mesoderm, and endoderm. As complete reorganization of cells has occurred during this phase, therefore cell division decreases in this stage.