This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Anatomy
[{'content': 'Which of the following statement is true regarding gastrulation? \nSelect and explain. \nA. Establishes all the three germ layers, B. Usually occurs at 4 weeks of gestation, C. Involves the hypoblastic cells of inner cell mass, D. Occurs at the caudal end of the embryo prior to its cephalic end', 'role': 'user'}, {'content': "Answer: A \nExplanation: Gastrulation is the formation process by which the 3 germ layers and axial skeleton are established in the embryo. It is the beginning of morphogenesis. It occurs during the third week of gestation. 3 germ layers which are formed includes ectoderm, endoderm and mesoderm.Ref: The Developing Human, Keith L. Moore, 7th Edition, Page 60 ; Langman's Medical Embryology, 8th Edition, Page 61", 'role': 'assistant'}]