The rapid increase in human population is mainly caused by a decreasing death rate (more rapidly than birth rate), an increase in average human age. This is due to revolution in medical fields by providing better medical facilities. It led to an increased birth rate also. So, option d is correct.

Explanation:


One of the factors contributing to the high increase in human population is the increase in average life span. Over the years, advancements in medical science, improved healthcare facilities, better sanitation, and access to clean water have led to a significant increase in life expectancy. People are living longer due to the prevention and treatment of diseases, reduction in infant mortality rates, and improved overall health conditions. This means that more individuals are surviving into reproductive age, leading to a higher number of births and ultimately increasing the population.


The availability of better medical facilities is another significant factor contributing to the high increase in human population. Improved medical technology, access to healthcare services, and the development of effective treatments and medicines have played a crucial role in reducing mortality rates. Medical advancements, such as vaccinations, antibiotics, and surgical procedures, have helped in preventing and curing diseases, thereby increasing the chances of survival. This has resulted in a higher population growth rate as more individuals are able to survive and reproduce.


A decrease in death rate is also a key factor contributing to the high increase in human population. Improved healthcare facilities, better nutrition, and advancements in medical science have led to a decline in mortality rates. Reduced deaths from diseases, accidents, and other causes have resulted in a larger number of people reaching reproductive age. This, in turn, leads to an increase in the number of births and ultimately contributes to population growth.


All the factors mentioned above - increase in average life span, better medical facilities, and decrease in death rate - work together and have a cumulative effect on the high increase in human population. These factors are interconnected and contribute to the continuous growth of the population. The combination of longer life expectancy, improved healthcare, and reduced mortality rates has resulted in a higher number of individuals surviving and reproducing, leading to an exponential increase in the global population.

In conclusion, the correct answer is option 'D' - all of these factors contribute to the high increase in human population.