What is the science behind the making of pop-up books?

Answer

The moveable parts of the pop up book are of often cut out by hand and are folded and glued by hand upon the printed pages. The cover is glued or sewn to the lining. Front and backs are often made up from board, which is just a heavier gauge paper than is used for the pages.

Explanation

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e) none of the above answers are correct

come closer and become far apart and become steam/gas