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': 'Malignant melanoma Which exists solely in vertical growth phase: \nSelect and explain. \nA. Follicular melanoma., B. Nodular melanoma., C. Granular melanoma., D. Hyperplastic melanoma.', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]