An example of a natural monopoly product is a.) a hair salon b.) a board game c.) airplane manufacturing d.) water service

i think that the answer is polishing peanuts

explanation:

the addition to geographic boundaries that might have  kept the people of the huang river civilization from traveling to far distance region is that they had learned about the other river valley civilizations but feared contact would bring invasion.

hope this .

plz give me brainliest!