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

Q: Passage: Bacteria can be used to make cheese from milk. The bacteria turn the milk sugars into lactic acid. The acid is what causes the milk to curdle to form cheese. Bacteria are also involved in producing other foods. Yogurt is made by using bacteria to ferment milk ( Figure below ). Fermenting cabbage with bacteria produces sauerkraut. Answer: lactic acid

A: Bacteria can be used to make cheese from milk. the bacteria turn the milk sugars into what?
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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: When a wave meets a barrier, it reflects and travels back the way it came. The reflected wave may interfere with the original wave. If this occurs in precisely the right way, a standing wave can be created. The types of standing waves that can form depend strongly on the speed of the wave and the size of the region in which it is traveling. Answer: reflected wave

A:
A standing wave is created when what type of wave interferes with the original wave?
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