The population decreased from 1840s until about 1970, largely be

The population decreased from 1840s until about 1970, largely because of _______.
A、a low birth rate
B、a high death rate
C、a low employment rate
D、a high emigration rate
【正确答案】：D
【题目解析】：从19世纪40年代到1970年，人口减少，主要是由于移民率高。