A child has two favorite glasses: a tall, skinny one with a picture of a giraffe on it and a short, fat one with a picture of a hippopotamus on it. When her mother pours her some milk using the "hippo" glass, the girls asks that the milk be moved into the "giraffe" glass because she is really thirsty. If the girls believes that simply transferring the milk into the taller glass increases the amount, she probably is capable of mental operations. is incapable of accommodation. is in the stage of formal operations. has not yet reached the concrete operational stage. Connor and Mandy are two unrelated 13-month-old infants.

Piaget's theory of cognitive development is a complete theory which focuses on the development and nature of human intelligence. According to Jean Piaget, children have four different stages in mental development. Piaget's lays importance on the nature of intelligence of the children and how children acquires that knowledge.

In the theory of cognitive development the concrete operational stage is the third stage in mental development. Children at the age of seven to eight are at the stage of applying logical reasoning to some real situations without being influenced by shape changes or appearance changes.

Thus, a child who believes that by transferring milk from a short fat glass to a tall skinny glass makes the amount of water to increase might have not reached her concrete operational stage yet.

Hence the answer is ---

has not yet reached the concrete operational stage.