To Explain New Fertility Patterns in European Countries, Demographers Have

To explain new fertility patterns in European countries, demographers have developed two new theories. In these two new theories, the decline of fertility and the importance of immigration are the main topics. What are the names of these two theories?

A) the first demographic transition and the second demographic transition
B) the third demographic transition and the fourth demographic transition
C) the second demographic transition and the third demographic transition
D) the new demographic transition and the new fertility transition
E) the transition of fertility behavior and the transition of immigration