这是一座移民城市——该市如今38%的人口为外来人口——移民以及他们的子代在美国经历了显著的向社会上层流动。
This is a city of immigrants 38 percent of the city's population today is foreign-born and immigrants and their children have historically experienced significant upward mobility in America.
由于人口的猛增或大量人口流动（现代交通工具使这种流动相对容易）造成的种种问题也会对社会造成新的压力。
Additional social stresses may also occur because of the population explosion or problems arising from mass migration movements—themselves made relatively easy nowadays by modern means of transport.
尤其在当今人口高度流动以及社会相互依存的环境下，大流行性病毒即使在暴发初期只导致原本健康的人出现轻微症状，也可能会造成破坏性后果。
Even a pandemic virus that initially causes mild symptoms in otherwise healthy people can be disruptive, especially under the conditions of today's highly mobile and closely interdependent societies.
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