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: Radiology
Thin radiolucent line which follows the outline of tooth is known as: 
Select and explain. 
A. Lamina dura, B. Nutrient canals, C. PDL, D. None of the above
C: PDL
Answer: C: PDL 
Explanation: Because the PDL is composed primarily of collagen, it appears as a radiolucent space between the tooth root and the lamina dura. This space begins at the alveolar crest, extends around the portions of the tooth roots within the alveolus, and returns to the alveolar crest on the opposite side of the tooth.
White and Pharoah, pg-134