GMAT Reading Comprehension (RC) | Few regions in Middle America are so important zoogeographically

Few regions in Middle America are so important zoogeographically as is the Isthmus of Tehuantepec, that neck of land connecting North America with Central America, separating the Pacific Ocean from the Gulf of Mexico by a distance of only about 220 kilometers, and forming a low break between the highlands of México and those of Central America. Before World War II the isthmus could be reached readily only by railroad or by ocean vessel to Salina Cruz or Coatzacoalcos; with the advent of roads,
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