<span>Federalism is the most important.
</span><span>I could be wrong but I gave it my best shot.
Hope this helps!!</span>
I believe the answer is: positive externality
Positive externality refers to The benefit that enjoyed by a third party when the first and second party are conducting a transaction.
When you receive a vaccines, you prevent yourself from becoming a host that could contaminate other people from getting the virus. In the example above, you and your children are the first and second party. And other children are the third party.
Answer is A.
it is the definition
