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。
Optical-based smoke alarms use light instead. They are slightly better at detecting the large smoke particles created by slow, smouldering fires. When such particles enter a chamber in the device, they scatter light from a small light source, which is then picked up by a photoelectric sensor.，更多细节参见heLLoword翻译官方下载
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欧美邮轮上有严格的Dress Code（着装要求），晚宴要正装，这在国内很难推行。不是大家穿不起，是觉得有点“装”，犯不着——我花钱是来享受的，不是来受罪的。，推荐阅读快连下载安装获取更多信息
Nearly every protection-related instruction -- far CALL, far JMP, far RET, INT, IRET, MOV to segment register, task switch -- needs to load a segment descriptor from the GDT or LDT. The 386 microcode centralizes this into a shared subroutine called LD_DESCRIPTOR, which reads the 8-byte descriptor from memory and feeds the high DWORD (containing Type, DPL, S, and P bits) to the Test PLA for validation.