Peace keeping for the United Nations is, at best of times and arduous task.

The correct answer is D. delicate.

Peacekeeping is a delicate task because

it involves dealing with complex political and social issues. Peacekeepers must be able to build trust and relationships with all parties involved in a conflict, and they must be able to operate in a difficult and dangerous environment.

The other options are not as accurate descriptions of peacekeeping. Laborious means requiring a lot of physical effort, and inconvenient means causing trouble or difficulty. Difficult means hard to do or understand, but it does not capture the complexity of peacekeeping.