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What is the best Duolingo for X thing to build?
Duolingo 开创了习惯养成的模式，哪些领域还缺一个“Duolingo for X”？这则 HN 讨论值得思考。
Duo opened up a new way of habit building and learning, that said, the options are endless... WHat is still up for grabs/Needed? Comments URL: https:/…