Final answer:
OPTION D.
When the birth rate is 40 and the death rate is 15, the population is increasing significantly as the number of births greatly exceeds the number of deaths.
Step-by-step explanation:
When the birth rate is at 40 per 1,000 people and the death rate is at 15 per 1,000 people, the population is increasing significantly. This is because the number of births far exceeds the number of deaths, leading to a net increase in the population. According to the demographic transition model (DTM), this situation may be characteristic of a country in the second stage, where death rates have fallen but birth rates remain high, resulting in a faster population growth.
Therefore, the correct answer to the student's question is: D. The population is increasing significantly.