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

It's difficult to understand his explanation.

The menu of this restaurant is various, making it difficult to choose.

He is an expert in statistics.

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

There is a beautiful mural painted on the side of this building.

He is an expert in sociology.

It's difficult to understand his explanation.

Health is very important.

His opinion is very important.