Aperson be cheaply prevented from using national defense, a(n) good. cannot; excludable cannot; nonexcludable can; excludable can; nonexcludable

The  answer is "Cannot; nonexcludable".

A public good refers to both non-rival, it means the utilization of a unit doesn't lessen those units accessible for others and  non-excludable which could not reasonably be expected on incorporate a few same time excluding others starting with this good. For instance an absence of education spare group keeping will be an immaculate government funded useful that shows both non excludable and non rival qualities. It will be non-excludable Similarly as it is not could reasonably be expected with avoid somebody starting with the profits of a absence of education nothing locale same time including others.

Also non-rival as particular case individual expending a absence of education allowed ward doesn't decrease the saves for others. 
Non-excludable good is a good whereby it is not conceivable should avoid people from utilizing the good, thereby making it challenging on limit get of the handy In light of value. 

Ithink it's a, but i might be wrong