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

Q: Passage: After the film is developed, any unexposed silver bromide must be removed by a process called "fixing"; otherwise, the entire film would turn black with additional exposure to light. Although silver bromide is insoluble in water, it is soluble in a dilute solution of sodium thiosulfate (Na2S2O3; photographer's hypo) because of the formation of [Ag(S2O3)2]3 ions. Thus washing the film with thiosulfate solution dissolves unexposed silver bromide and leaves a. Answer: fixing

A: After the film is developed, any unexposed silver bromide must be removed by a process called what?
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Q: Passage: Improving crops by selecting for certain genetic traits. The desired traits promote productivity. Recently, genetically engineered crops have been introduced. Answer: promotes productivity

A: What is the advantage of selecting for certain genetic traits for crops?
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Q: Passage: Opposite charges attract, and like charges repel. Answer: attract

A:
What do opposite charges do to one another?
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