Answer:
differentiating
Step-by-step explanation:
This is a classic kind of Piaget task. The point of doing such tests is to see if sameness is maintained if an operation alters a shape. For example, if two glasses are identical and filled to the same height, the child is then asked which glass has more in it. He/she must be able to say they are both the same. If not, the test terminates.
Then one of the glasses of water is poured into a different shaped glass and again the child is asked again which glass has more in it. Usually a child under 4 will pick the tallest one as having more in it. Very few can transfer sameness.
The answer that goes in the blank is differentiating operations.