The zone of proximal development refers to
a) the notion that moral reasoning is based primarily on the evidence of what is "right" and what is "wrong" as dictated by society's rules.
b) the skills children cannot yet perform on their own, but can perform if they have some from someone who has already attained those skills.
c) the understanding that the volume of a particular liquid remains the same even if the container it is poured into is different in appearance from the original container.
d) the outward verbalizations a young child makes when working through a challenging task.