As Shawn and his father, Carlos, put together a puzzle for the first time, Carlos begins by showing Shawn how to locate the outside pieces of the puzzle first. Once Shawn starts to get the idea, Carlos gradually withdraws his support, allowing Shawn to take more responsibility. Carlos is demonstrating Vygotsky's concept of:. a) sensorimotor support. b) overimitation. c) optimal reinforcement. d) scaffolding