Given a scientific passage and an answer, generate a question for the given answer.
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Question: Passage: Another scientist, who worked with Becquerel, actually came up with the term radioactivity . The other scientist was the French chemist Marie Curie. She went on to discover the radioactive elements polonium and radium. She won two Nobel Prizes for her discoveries. You can learn more about Marie Curie at this URL: http://nobelprize. org/nobel_prizes/physics/laureates/1903/marie-curie-bio. html. Answer: marie curie

Answer: What french chemist discovered the radioactive elements polonium and radium?

Question: Passage: Structure of the trp operon. The trp operon is composed of 5 structural genes, 1 regulatory gene and other regulatory sequences, including the promoter, operator and leader sequence. Within the leader sequence is the attenuator region. In the presence of tryptophan, the structural genes are not transcribed. Answer: they are not transcribed

Answer: What happens to structural genes in the presence of tryptophan?

Question: Passage: the distance light can travel in one year, 9.5 trillion kilometers. Answer: light

Answer:
What travels 9.5 trillion kilometers a year?