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Technology history: How can a plane fly that fast and go that high?
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Social history: Why do people go to pre-school at 3?
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Social history: Why do people go to pre-school at 3?
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Social history: Why do people stay in pre-school for 3 years and go to primary school at 6?
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Social history: Why do people travel to other countries?
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Social history: Why do people go to other countries to study?