The correct answer is - a. human demography.
The human demography is a sub-discipline of geography. It also involves, and is heavily orientated towards the statistics. It is study that has its focus on the human populations and their characteristics and trends, such as number of population, birthrates, mortality rates, population density, sex representation, migrations, education, as well as the reasons why people live in a particular place, and the reasons why they don't live in a particular place.
The statistical data from the human demography is essential for the functioning and future planning of every country in the world.
Heat in Earth's core is produced by pressure.
I would think social customs
