Vygotsky's Zone of Proximal Development Is Best Characterized by Which

Vygotsky's Zone of Proximal Development is best characterized by which example?

A) A child is unable to understand a new mathematical concept regardless of the teacher's help.
B) A child figures out how to correctly spell a four-syllable word alone.
C) A child counts to five, but the teacher helps the child count a few more numbers to 10.
D) A parent tests a child's zone of proximal development by asking his/her child to calculate 2 + 2 quickly.
E) Children that have reached the formal operational stage have outgrown limits in their zone of proximal development.