At various times, the nations that constitute the organization of petroleum exporting countries (opec) have restricted the supply of oil to increase their profits. this is an example of:

a the unsuitability of some goods for efficient management by markets.
b regulating self-interest.
c individual actions whose side effects are not properly taken into account by the market.
d one party preventing mutually beneficial trades in an attempt to capture a greater share of resources for itself.

d. one party preventing mutually beneficial trades in an attempt to capture a greater share of resources for itself.

Explanation:

In the  Organization of Petroleum Exporting Countries (OPEC), there is a one very strong party. This party exerts monopoly and greater say in policy making and due to its clout it tries to prevent trade which could fetch benefits just because it wants greater share in the overall profit.

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