The correct option is A Thyroid
The three germ layers (the ectoderm, the mesoderm and the endoderm) are in place at the end of gastrulation and gives rise to different parts of the organism. The innermost layer is the endoderm which gives rise to various parts of the body such as the epithelial lining of the gastrointestinal and respiratory tract, the parenchyma of tonsils, liver, thymus, thyroid, parathyroids and pancreas. Thus, the correct answer is option A.