This week andrea is babysitting her younger sisters, cassy, who is the youngest, and nikki. andrea fixes them both a glass of their favorite juice except that cassy's glass is taller and nikki's is wider and shorter. andrea anticipated that nikki would complain, but she did not. when andrea asked nikki why, nikki replied that the glasses held the same amount. nikki is in which stage of cognitive development according to piaget's theory
