Brendan Is Just Learning to Walk

Brendan is just learning to walk.He can take a few steps by himself if he uses both hands to hold on to a piece of furniture for support,but he can walk out into the middle of the room only if one of his parents holds his hands.Which of the following represents the lower limit of Brendan's zone of proximal development (ZPD) for walking?

A) Brendan learning to run after he has mastered walking
B) Brendan going back to crawling when he becomes frustrated by trying to walk
C) Brendan walking alone by holding on to a piece of furniture with one hand
D) Brendan learning to walk by having his parents follow along behind to support him when he loses his balance