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

Passage: Carbohydrates, proteins, and nucleic acids are large molecules (macromolecules) built from smaller molecules (monomers) through dehydration reactions. In a dehydration reaction, water is removed as two monomers are joined together. Answer: water
In a dehydration reaction, what is removed as two monomers are joined together?