He moved agilely to avoid the enemy bullets.

The enemy aircraft invaded our airspace.

We are ready to invade enemy territory.

We are conducting training to devise strategies against hypothetical enemies.

His grandfather was a member of the special attack squad.

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.

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