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: Surgery
The "red line" in winter's classification of impacted teeth represents: 
Select and explain. 
A. The depth at which the impacted teeth is located, B. The angulation of the 2nd molar, C. The summit of the alveolar bone covering the impacted tooth, D. Relation of the 3rd molar to the ramus
A: The depth at which the impacted teeth is located
Answer: A: The depth at which the impacted teeth is located 
Explanation: None