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New World Epidemics
A huge loss of life resulted from the introduction of Old World diseases into the Americas in the early sixteenth century. The inhabitants of the Americas were separated from Asia, Africa, and Europe by rising oceans following the Ice Ages, and as a result, they were isolated by means of this watery barrier from numerous virulent epidemic diseases that had developed across the ocean, such as measles, smallpox, pneumonia, and malaria.
Pre-Columbian Americans had a relatively disease-free environment but also lacked the antibodies needed to protect them from bacteria and viruses brought to America by European explorers and colonists. A devastating outbreak of disease that strikes for the first time against a completely unprotected population is known as a virgin soil epidemic.
Virgin soil epidemics contributed to an unbelievable decline in the population of native inhabitants of the Americas, one that has been estimated at as much as an 80 percent decrease of the native population in the centuries following the arrival of Europeans in the Americas.
The words they – that – them - one in the passage refer to:

a

Epidemic diseases / a disease-free environment / the antibodies / a virgin soil epidemic

b

Rising oceans / this watery barrier / bacteria and viruses / the population of native inhabitants

c

The ice ages / the ocean / European explorers and colonists / the arrival of Europeans

d

The inhabitants / virulent epidemic diseases / pre – Columbian Americans / an unbelievable decline

e

The ocean/ the ice ages/ this watery barrier and the arrival of Europeans

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