Higher-level modules are the ones that operate on a higher conceptual level (i.e. algorithms, domain logic, business rules, etc). In other words, they’re more abstract and they govern “what” the application is supposed to do. On the other hand, modules that contain more implementation-specific code (e.g. hardware, I/O, network, etc) are said to be lower-level.
歷任總統通常會在橢圓形辦公室或其他正式場合向全國發表演說，解釋其派遣軍隊作戰的理由。喬治·W·布什（George W Bush）總統曾多次在白宮發表談話，為伊拉克與阿富汗戰爭辯護。奧巴馬總統在第一任期早期，也曾詳細說明增兵阿富汗的原因。
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“When people get hurt around our products, we need to take every ounce of education from it that we can,” Jacob Zeiger, a senior air-safety investigator at Boeing, told me, when I visited the Boeing facility this past December. “These technical findings are sacred.” Within hours of any major incident involving a Boeing plane, Zeiger and his team are notified, and they may spend a week to ten days studying the damage and interviewing the crew, piecing together what went wrong. In 2008, for instance, the engines on a 777 stopped responding, and it crash-landed short of a runway in London, shearing off its landing gear. Afterward, a team of investigators re-created the plane’s fuel system in a Boeing lab. A small heat-exchange unit, they found, had accumulated ice during the flight. Every 777 has since been retrofitted with a new version of the unit. Thanks to decades of such refinements, today’s jets may be the world’s most reliable machines. Flying in them is less likely to kill you than walking on staircases.
Communications System, which was superficially a large terminal that, depending