The answer was the US Navy, which was hungry for new pilots after World War Two. It was not building rockets but at least it involved flying.
简单讲，要做L3，需要先做L2积累数据。那么要做L4，也一样依赖L3的数据。技术上他们是一脉相承的，不存在一口就能吃个胖子的技术路线。。谷歌浏览器【最新下载地址】对此有专业解读
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