Answer: (i), (iii) and (iv)
Explanation:
PPCo is able to provide the entire needs of the county and and has been in operations for a few years gaining loyal customers and controlling the market. Any company that will want to come in will have to fight them for market dominance and as such will have a smaller market share than PPCo.
As PPCo is meet the demands of everyone in the county, they are most likely experiencing Economies of Scale. This means that they are making more revenue thereby driving total cost down as the fixed costs remain the same but Revenue climbs. This classifies them as a Natural Monopoly because Natural Monopolies experience Economies of Scale and declining average total costs.