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Given a scientific passage and an answer, generate a question for the given answer.

Passage: Example Problem: The density of steel is 9000. kg/m 3 and the density of water is 1000. kg/m 3 . If a cube of steel that is 0.100 m on each side is placed in a tank of water and weighed while under water, what is the apparent weight of the cube?. Answer: head
Output:
Cephalization refers to the development of what anatomical region, which evolved at the same time as bilateral symmetry in animals?