The best answer is:
D. The population likely is growing.
A total fertility rate (TFR) of 4.0 indicates that, on average, a woman is having 4 children over her lifetime, which is generally above the replacement level of approximately 2.1 children per woman needed to maintain a stable population size in the absence of immigration. Therefore, a TFR of 4.0 suggests that the population is likely to grow.