This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Introduction and gametogenesis., Subject name: Anatomy
[{'content': 'Which of the following is the origin of the mitochondrial DNA of all human adult cells? \nSelect and explain. \nA. Paternal only, B. Maternal only, C. A combination of paternal and maternal, D. Either paternal or maternal', 'role': 'user'}, {'content': "Answer: B \nExplanation: The mitochondrial DNA of all human adult cells is of maternal origin only. In human feilization, the entire sperm enters the secondary oocyte cytoplasm. However, sperm mitochondria degenerate along with the sperm's tail. Therefore, only mitochondria present within the secondary oocyte (maternal) remain in the feilized zygote.", 'role': 'assistant'}]