The pollution of this river has become a serious problem.

This river has been polluted by the waste from the factory.

In Buddhism, it is considered important to remove the dirtiness of the mind.

This problem is very serious.

Do you understand the seriousness of this problem?

We often have picnics by the river on weekends.

Can you answer this question?

We often have picnics by the river on weekends.

We have a picnic by the river every weekend.

The environmental issues are becoming more serious.