The classic examples of natural monopolies over the years have been

A) agriculture.
B) auto manufacturers.
C) public utilities.
D) retail trade.

Natural Monopolies

Market conditions where a single supplier is the most efficient (due to high infrastructure costs or other barriers) in providing a particular good or service.

Public Utilities

Companies that provide essential services to the public such as water, electricity, and telecommunications, often subject to government regulation due to their nature of operation.