Concept: OPEC is a cartel of petroleum-exporting countries, and its main economic objective is to control/maximise revenue from crude oil.Explanation:OPEC coordinates oil production and pricing policies among member countries.The ultimate aim of this coordination is to present a common front and influence crude oil prices favourably for members.Unity, quota rules, and political stability are only means or side objectives, not the primary goal.Answer: A. present a united front for the purpose of raising prices of crude oil