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 “If we can set it up so you can’t unlock your phone unless you’ve got the right fingerprint(指纹),” Barack Obama asked last Tuesday, “why can’t we do the same thing for our guns?” For this reasonable-sounding question, the president was applauded throughout the media. As it happens, though, there is a good answer to this question: there is no market for guns that work just some of the time. Guns are simple things designed to operate as easily and reliably as possible. The introduction of electronics eats away this simplicity, and to a degree that is absolutely unaccept上海距北京约1500km，火车运行速度约为200km/h．2007年我国铁路第六次大提速后，上海至北京的火车速度提升为300km/h，则现在乘坐火车从上海到北京可比原来节省    h．