Which of the Following Examples Illustrates Vygotsky's Notion of the Zone

Which of the following examples illustrates Vygotsky's notion of the zone of proximal development?

A) At T-ball Timon can hit the ball from the tee on his own.His father is now teaching Timon how to swing at a ball being tossed.He is helping Timon to swing the bat as the pitcher lobs the ball.
B) Lily perseveres with putting together a difficult puzzle, rejecting all offers of help.
C) Although Yao Ming is only 4 years old he can already read.
D) Manuel's mother does not feel Manuel is trying hard enough at school, so she will not allow him to have a snack after school unless he gets a perfect score on his homework.