He likes living in a big city.

In urban areas, smog has become a serious problem.

This problem is very serious.

Do you understand the seriousness of this problem?

Can you answer this question?

The environmental issues are becoming more serious.

Environmental issues are becoming more serious day by day.

A new approach is needed to solve this set of problems.

The main problem with this project is the lack of communication.

This question text is too difficult, it's hard to understand.