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
Which of the following is used as a bio-degradable membrane in "guided tissue regeneration" process? 
Select and explain. 
A. Polylactic acid, B. Poly tetrafluoroethylene, C. Millipore, D. Core membrane
A: Polylactic acid
Answer: A: Polylactic acid 
Explanation: None