Answer: d. All of the above are examples of the principle that trade can make everyone better off.
Step-by-step explanation:
We make a trade when we exchange services in which we benefits while the other part or the other person also benefit.
Americans buying socks from china that means the business from China is benefitting financially whilst the people in America are benefiting from using this product .
Drinks bought in Maine from Florida befits the Florida business whilst people in Maine are also benefiting from buying and enjoying these drinks.
A kid from next door mowing the lawn will benefits financially as the neighbor pays him whilst the neighbor is benefiting from his service of having his lawn mowed .