Answer: Ectoderm
Explanation: Ectoderm develops into to the parts of the brain, nervous system and the skin. The brain develops from the most basic part to the most complex one. Firstly the brain stem develops, followed by the cerebellum, the limbic system and the cerebral cortex.
Endoderm forms the lining of the gut and other internal organs. Mesoderm forms skeletal system, circulatory system and the muscles. Trophoblast forms outer layer of blastocyst, which gives nutrients to the embryo and develops into large part of placenta. Blastocyte forms the embryonic stem cells and capable of forming all types of cell within the embryo.