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: Dental
[{'content': 'Long depression or valley between ridges and cusps, the inclines of which meet at an angle is known as: \nSelect and explain. \nA. Sulcus., B. Groove., C. Lobe., D. Fossa.', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]