Which of the following is a major function of OPEC?

The correct answer focuses on the primary role of OPEC (Organization of the Petroleum Exporting Countries), which is to coordinate and unify the petroleum policies of its member countries to ensure the stabilization of oil markets. This is crucial for securing a steady income for the producing nations and ensuring a fair return on investment in the petroleum industry.

OPEC achieves this by managing oil production levels among its member nations, which helps to influence global oil prices and supply. By agreeing on production quotas, OPEC aims to balance supply and demand in the global market, which is vital for maintaining economic stability among its members as well as globally.

The other options do address important global issues but do not pertain to OPEC's primary objectives. For instance, the regulation of military conflicts is outside the organization’s scope, as is the direct promotion of environmental sustainability, although OPEC does take several factors, including environmental considerations, into account in discussions. Developing new technologies is primarily the focus of individual member countries or private sectors rather than OPEC as a collective organization focused on oil production coordination.