I was surprised at his quick progress.

I am surprised at the quickness of this project's progress.

The population of Japan is decreasing.

Demography is a branch of social science that studies the structure, distribution, and changes in human population.

Tokyo is the city with the highest population density in Japan.

The next census will be conducted next year.

Demography is a part of social science that studies the structure, evolution, and problems of human population.

Looking at the population pyramid, you can see that this country is aging.

Demography is an important tool for understanding various aspects of society.