Answer:
D
Step-by-step explanation:
A would be incorrect as not all natural monopolies are set up in the primary sector. One such example is a state monopoly in electricity, which is in the secondary and/or tertiary sector.
B would be incorrect as natural monopolies need government regulation to exist and if they are producing where AR=AC, then they will need subsidies.
C would be incorrect as it is not always the case that the firm is voted into existence by voters as it may just be goernment set-up.
D would be correct as having more than one business in the market in question would negate the economies of scales that a natural monopoly has and by increasing competition the cost advantage would lead to higher prices being charged which the consumer will end up paying.