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19C〜北米綿花↑
∵1.ホイットニーの綿繰り機
∵2.＿＿＿＿＿＿＿＿＿

世界史

Optimized studying based on the forgetting curve vastly improves memorization. - What is reminDO?

Memorize

Evagreen

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