Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: Humans learn behaviors through conditioning, as well. A young child might learn to put away his toys by being rewarded with a bedtime story. An older child might learn to study for tests in school by being rewarded with better grades. Can you think of behaviors you have learned by being rewarded for them?. Answer: conditioning

Answer: How do humans learn behaviors?

Question: Passage: Cloud types include cirrus, stratus, and cumulus. Answer: clouds

Answer: Cirrus, stratus, and cumulus are types of what?

Question: Passage: When lactose is available, a lactose metabolite called allolactose binds to the allosteric site on the repressor. This interaction causes a conformational change in the repressor shape and the repressor falls off the operator, allowing RNA polymerase to bind to the promoter and initiate transcription. Allolactose is called an inducer because it turns on, or induces the expression of the lac genes. Answer: allolactose

Answer:
Which inducer turns on the expression of the lac genes?