Final answer:
The core of the teacher's assumption lies in the nature vs. nurture debate, which involves the relative contributions of genetic inheritance and environmental factors to human development. Correct option is C.
Step-by-step explanation:
The teacher's assumption that a student should be able to play the piano because their parents are musicians is based on the nature vs. nurture debate. This debate considers the extent to which particular aspects of behavior are a product of either inherited (nature) or acquired (nurture) characteristics.
The teacher's surprise reflects an expectation that musical ability is inherited, suggesting that the child should naturally acquire these skills from their parents. However, according to Vygotsky's sociocultural theory of development, a child's abilities are also significantly shaped by their cultural background and social interactions, not just by genetics.