this is a multiple choice question:

A natural monopoly is one in which: a) a firm has a monopoly through exclusive ownership of some natural resource that is critical in production (e.g., a spring that is used to produce bottled water); b) a single firm can satisfy the market demand at a lower average cost than what the average costs of firms would be if several firms operate in the market; c) there are increasing returns from scale that are substantial, which gives an advantage to whichever firm is the first to grow large; d) a firm has an inherent competitive advantage (such as managerial talent) that allows it to set its price below those of other firms; e) b) and c) are both true