Little Jimmy (4 years old) asks his Mom for more milk. They’…

Little Jimmy (4 years old) asks his Mom for more milk. They’re all out of milk, so out of sight, she pours the milk from a short fat glass into a tall thin glass. Jimmy is satisfied and gives her a cheerful “Thanks Mom!”  Jimmy is in the _____ stage, according to Piaget and is failing to understand the principle of ________.