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 of the following demonstrates highest correlation between variables? \nSelect and explain. \nA. r = + 0.25, B. r = + 0.5, C. r = - 0.75, D. r = + 2', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]