Demographers who once believed that the U.S population would stabilize between 290 and 300 million people now believe that it will stabilize at around 390 million people because its________________?

Demographers who once believed that the U.S population would stabilize between 290 and 300 million people now believe that it will stabilize at around 390 million people because its________________?

A. overall birth-rate will increase significantly in the early part of the new century
B. life expectancy at birth will shortly increase to nearly 100 years of age
C. immigration rate is expected to remain high
D. all of the above