Problem: What city built the first underground train network?
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A: london

Problem: The film 1953 Calamity Jane produced which hit for Doris Day that reached #1 on the Billboard charts in 1954?
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A: secret love

Problem: In 18th/19th century England, mercury was used in the production of felt, which was used in the manufacturing of hats. Some workers in these factories developed dementia because of mercury poisoning. What expression for insanity has this etymological origin?
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A: mad as hatter

Problem: Which element has atomic number 8?
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A:
oxygen