这位医学先驱或许从未想过，自己的脱发问题，会在数千年后的今天，催生出一个规模千亿的庞大市场。据不完全统计，已有超过3.38亿国人面临脱发困扰，相当于每4个国人中就有1人被脱发问题所困扰，且脱发人群还呈现出持续年轻化的鲜明趋势，越来越多的年轻人加入“防脱大军”。
then we must meet the goal that a + b is also threeven.
，更多细节参见爱思助手
The first thing is what it tells us about who J. D. Vance is. The bank teller story—how ATMs were predicted to increase bank teller unemployment, but in fact did not—isn’t a story you’ll hear from politicians; in fact, for a long time, Barack Obama would claim, incorrectly, that ATMs had decreased the number of bank tellers, in order to suggest that the elevated unemployment rate during his presidency was due to productivity gains from technology. I’ve never heard a politician cite the bank teller story before: but I have seen the bank teller story cited in a lot of blogs. I’ve seen it cited, for example, by Scott Alexander and Matt Yglesias and Freddie deBoer; and I’ve heard it, upstream of the humble bloggers, from such fine economists as Daron Acemoglu and David Autor. The story of how ATMs didn’t automate bank tellers is, indeed, something of a minor parable of the economics profession. You can see it encapsulated in this wonderful graph from the economist James Bessen:
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