One of the reasons of rapid growth of world population is
improved social and medical facilities
stable government
rainfall and its reliability
agricultural system practised
Correct answer is A
The provision of modern and improved medical and social facilities to area tends to attract more population concentration to another.
Other options are wrong because the government being stable does not determine population growth, social amenities provided by the government is the only factor that can make the population growth low, either rainfall or not, people will migrate and reproduce.
The agricultural system practical in an area also does not determine rapid population growth. Either mono-cropping or mixed farming is practiced population will always grow.