This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Abdomen and pelvis, Subject name: Anatomy
[{'content': 'Vaginal epithelium is a derivative of \nSelect and explain. \nA. Mesoderm of urogenital sinus, B. Endoderm of urogenital sinus, C. Mesoderm of genital ridge, D. Endoderm of genital ridge', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The wall of the vagina from the lumen outwards consists firstly of the mucosa of non keratinized stratified squamous epithelium with an underlying lamina propria of connective tissue, secondly a layer of smooth muscle with bundles of circular fibers internal to longitudinal fibers, and thirdly an outer layer of connective tissue called the adventitia. ref - BDC 6e vol2 pg395', 'role': 'assistant'}]