Answer: Option (A) is correct.
Explanation:
The national defense of a nation is considered as a public good. We know that public good has two major characterstics that are non-rival and non-excludable.
Non-rival goods refers to the satisfaction level or the utility obtained from a particular good will not reduce from one person's consumption. The amount of good available to other individuals remains the same.
Therefore, if one person is enjoying national defense then this will not reduce the satisfaction level obtained from the national defense for the other individuals.