Why Is National Defence a Classic Example of a Public

Multiple Choice

Why is national defence a classic example of a public good

A) Private security services are very difficult to find.
B) It is difficult to exclude people from receiving the benefits from national defence once it is provided.
C) Everyone agrees that some level of national defence is important, but only the government knows the optimal amount.
D) If individuals were required to purchase their own armoured tank, there wouldn't be enough tanks to go around.