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
Your examination reveals a probing pocket depth of 6 mm on the facial surface of tooth 30. The free gingival margin is 2 mm apical to the CEJ (there is 2-mm recession on the facial). How much attachment loss has there been on the facial of this tooth? 
Select and explain. 
A. 6 mm, B. 2 mm, C. 8 mm, D. 4 mm
C: 8 mm
Answer: C: 8 mm 
Explanation: When the free gingival margin is apical to the CEJ, recession has occurred. Attachment loss is the measure from the CEJ to the base of the periodontal pocket. With the free gingival margin 2 mm apical to the CEJ and the probing pocket depth measurement 6 mm, there has been 8 mm loss of attachment.