the crash of egypt air flight 804,which terrorists may have downed over the mediterranean sea,provides another tragic reminder of why.

主干：the crashprovides another tragic reminder
后置定语：后置定语的构成（n+介词+n）
the crash of egypt air flight 804。
provides another tragic reminder of why。
非限制性定语从句：which terrorists may have downed over the mediterranean sea,
翻译：埃及航空804号班机的坠毁，以悲剧的形式再次提醒我们为什么这么做。它可能被

恐怖分子击落于地中海。