He encountered the enemy on the battlefield.

He likes to take a walk in the park at dusk.

Linear programming is a part of operations research and is used to find the optimal solution.

Paying the urban planning tax is a citizen's duty.

The United Nations Environment Programme is providing solutions to global environmental problems.

We should always remember the power of Kannon in difficult times.

He said, 'It's difficult to make a life,' explaining the phrase 'When a man steps over the threshold, he has seven enemies.'

This ancient proverb, 'know the other side and yourself, and you will not be in danger in a hundred battles', teaches us the importance of understanding ourselves and others.