In Global Economics for Managers, monopolies arise when barriers to entry prevent competitors from entering a market. Two common barriers are control of a key resource and economies of scale, making options A and B correct.

When a single firm owns a unique or scarce resource, competitors cannot produce the good without access to that resource. Economies of scale create monopolies when one firm can produce at a lower average cost than multiple firms due to high fixed costs.

Options C, D, and E promote competition rather than monopoly.

Thus, options A and B correctly identify monopoly-creating barriers to entry.