In the context of Lev Vygotsky's theory of socio-cultural development, analyzing the concepts of 'Zone of Proximal Development' (ZPD) and 'Scaffolding', which of the following statements most accurately defines the foundational and functional relationship between the two?

According to Lev Vygotsky's socio-cultural theory, the 'Zone of Proximal Development' (ZPD) expresses the gap that exists between a child's independent problem-solving (actual developmental level) and problem-solving under adult guidance or collaboration with a More Knowledgeable Other (potential developmental level). On the other hand, 'scaffolding' refers to the temporary and flexible support provided by skilled teachers or peers to help the learner cross the boundaries of the ZPD.