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: Pathology
[{'content': 'A critical factor in the regulation of craniofacial development \nSelect and explain. \nA. Sonic hedgehog (SHH), B. Fibroblast Growth factor (FGFz), C. Wingless Drosophila melanogaster segment — Polarity gene (Wnt), D. Bone Morphogenic Protein (BMP)', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]