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': 'Which one of the following complexes of periodontal micro-organisms is associated with bleeding on probing? \nSelect and explain. \nA. Red Complex, B. Orange Complex, C. Green Complex, D. Yellow Complex', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]