Let's say you are recreating a classic test in developmental psychology where you pour a liquid from one container into a taller, thinner container Some children think the amount of liquid changes when you do this and some think the amount stays the same. Piaget used this test to separate children between which two stages of cognitive development? 

 A) sensorimotor and preoperational

B) preoperational and concrete operations

C) concrete operations and formal operations 

D) sensorimotor and concrete operations