The correct option is A Ectoderm
By the process of gastrulation, three germ layers are formed in the developing embryo and which gives rise to the different parts and tissues of the body. The inner cell mass differentiates into an outer layer called ectoderm and an inner layer called endoderm. The middle layer called the mesoderm appears between the ectoderm and endoderm.
The ectoderm gives rise to the central nervous system (brain and spinal cord), the peripheral nervous system, neural tube, the sensory epithelia of the eye, ear and nose, epidermis, mammary gland etc.
Mesoderm gives rise to connective tissue (bone and cartilage), kidneys, heart walls, spleen etc.
The endoderm gives rise to the epithelial lining of the gastrointestinal and respiratory tract; urinary bladder and urethra, parenchyma of the thyroid, liver, pancreas etc.