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1
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gravity
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Space exploration in the US
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Gravity is a major obstacle that must be overcome for successful space exploration.
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4
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2
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moon landing
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Space exploration in the US
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The 1969 moon landing symbolized a major accomplishment for US space exploration.
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4
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3
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space suit
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Space exploration in the US
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Space suits are necessary for astronaut survival and protection in the vacuum of space during US space missions.
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4
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4
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rocket launches
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Space exploration in the US
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The US culture values rocket launches as powerful and awe-inspiring events that mark the beginning of space exploration.
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2
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