Problem 10: When inventors do not patent in a given year, they lack data entries; we know their patent count is zero, but their city is unrecorded. M21 interpolates these observations for gaps of one or two years to partially capture extensive margin effects.
正如先前提示栏目所述，这款源自《纽约时报》的热门文字游戏旨在检验体育迷的知识储备。
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