This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General Embryology 1, Subject name: Anatomy
[{'content': 'Which of the following are components of the definitive chorion? \nSelect and explain. \nA. Extraembryonic somatic mesoderm and epiblast, B. Extraembryonic somatic mesoderm and cytotrophoblast, C. Extraembryonic somatic mesoderm and syncytiotrophoblast, D. Extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast', 'role': 'user'}, {'content': 'Answer: D \nExplanation: The definitive chorion consists of three components: extraembryonic somatic mesoderm, cytotrophoblast, and syncytiotrophoblast. The chorion defines the chorionic cavity in which the embryoblast is suspended and is vital in the formation of the placenta.', 'role': 'assistant'}]