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
Malignant melanoma Which exists solely in vertical growth phase: 
Select and explain. 
A. Follicular melanoma., B. Nodular melanoma., C. Granular melanoma., D. Hyperplastic melanoma.
B: Nodular melanoma.
Answer: B: Nodular melanoma. 
Explanation: None