This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Development of GU system and Neuro-vascular supply of pelvis & perineum, Subject name: Anatomy
Trigone of Urinary Bladder develops from ? 
Select and explain. 
A. Mesoderm, B. Ectoderm, C. Endoderm of urachus, D. Endoderm of urogenital sinus
A: Mesoderm
Answer: A: Mesoderm 
Explanation: Trigone is derived from mesoderm although bladder is endodermal in origin. Intermediate mesoderm forms the Genito urinary system. Endoderm forms the urogenital sinus which forms urinary bladder and urethra.