[单项选择]Increasingly, historians are blaming diseases imported from the Old World for the great disparity between the native population of America in 1492--new estimates of which jump as high as 100 million, or approximately one-sixth of the human race at that time--and the few million full-blooded Native Americans alive at the end of the nineteenth century. There is no doubt that chronic disease was an important factor in the sharp decline, and it is highly probable that the greatest killer was epidemic disease, especially as manifested in virgin-soil epidemics.
Virgin-soil epidemics are those in which the populations at risk have had no previous contact with the diseases that strike them and are therefore immunologically almost defenseless. That virgin-soil epidemics were important in American history is strongly indicated by evidence that a number of dangerous maladies--smallpox, measles, malaria, yellow fever, and undoubtedly several more--were unknown in the pre-Columbian New World.
A. provide support for a hypothesis.
B. reconcile opposing viewpoints.
C. refute a common misconception.
D. analyze an argument in detail.

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