The correct answer is option 'A' - Once a year.

Explanation:
The General Assembly of the United Nations (UN) is the main deliberative, policymaking, and representative organ of the organization. It is composed of all 193 member states of the UN, and each member state has one vote. The General Assembly meets in a regular session to discuss and make decisions on various global issues.

Frequency of General Assembly Sessions:
The General Assembly meets in a regular session once a year. This session usually starts in September and lasts for several months, typically until December. During this session, all member states have the opportunity to address the General Assembly and present their views on global issues, as well as propose resolutions for consideration.

Key Functions of the General Assembly:
1. Setting International Agendas: The General Assembly sets the international agenda by discussing and addressing significant global issues such as peace and security, sustainable development, human rights, and international law.

2. Making Decisions: The General Assembly makes decisions on various matters, including adopting resolutions and declarations. These decisions are not legally binding, but they carry significant political weight and shape the UN's policies and actions.

3. Electing Members: The General Assembly elects members to various UN bodies, including the Security Council, Economic and Social Council, and other specialized agencies and committees.

4. Budget Approval: The General Assembly approves the UN's budget and financial matters, ensuring the organization's smooth functioning.

5. Reviewing Reports: The General Assembly reviews reports from other UN bodies, such as the Secretary-General's annual report, which provides updates on the organization's activities and initiatives.

6. Promoting International Cooperation: The General Assembly promotes international cooperation by fostering dialogue, facilitating negotiations, and encouraging collaboration among member states.

Conclusion:
The General Assembly of the United Nations meets in a regular session once a year to discuss and make decisions on various global issues. It plays a crucial role in setting international agendas, making decisions, and promoting international cooperation among member states.