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': 'The learning theory of digit sucking was proposed by \nSelect and explain. \nA. Davidson, 1967, B. Sears and Wise, 1982, C. Johnson and Larson, 1993, D. Sigmond Freud, 1905', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The learning theory: Davidson (1967)\nThis theory advocates that non-nutritive sucking stems from an adaptive response.\nThe infant associates sucking with such pleasurable feelings as hunger. These events are recalled by sucking the suitable objects available, mainly thumb or finger.', 'role': 'assistant'}]