Which of the following is an example of a collective good?

The correct choice is national defense, as it exemplifies a collective good. A collective good is characterized by two main features: it is non-excludable and non-rivalrous. Non-excludable means that no one can be effectively excluded from using the good, while non-rivalrous means that one person's use of the good does not diminish its availability for others.

In the case of national defense, once it is provided, every citizen benefits from the protection it offers without being able to be excluded from these benefits. The provision of national defense does not decrease based on how many individuals utilize it, making it a quintessential example of a collective good.

On the other hand, the other options provided do not possess these characteristics. Pizza, as a privately provided good, can be limited to paying customers, and its consumption by one person reduces availability for others. Pay-per-view TV also restricts access based on payment, making it excludable and rivalrous. While city streets might seem to be a public resource, they can still be congested or limited in terms of usage at certain times, unlike national defense, and thus do not fit the definition of a collective good as neatly as national defense does.