Three-year-old Sharon can solve four-piece jigsaw puzzles on her own but needs her parents' help to solve six-piece jigsaw puzzles. Which of the following represents the upper limit of Sharon's zone of proximal development (ZPD) for solving such puzzles? Multiple Choice Sharon solving six-piece puzzles with her parents' help Sharon helping her 2-year-old brother solve four-piece puzzles Sharon moving on to 10 -piece puzzles Sharon mastering four-piece puzzles Prev