试题题干
（）epidemics are thought to have caused the greatest loss of life for indigenous populations, although estimates of the pre-Columbian population of what today constitutes the US vary significantly, from 1 million to 18 million.
参考答案
正确答案：
试题解析
尽管对前哥伦布时代的人口占现今美国人口比重的估算值变化很大，从100万到]800万，但是，肆虐的天花仍被认为是大量土著人丧生的罪魁祸首。答案为A。