The correct answer is A. 1945.
The United Nations (UN) is an international organization founded in 1945 after the Second World War by 51 countries committed to maintaining international peace and security, developing friendly relations among nations and promoting social progress, better living standards and human rights. Due to its unique international character, and the powers vested in its founding Charter, the Organization can take action on a wide range of issues, and provide a forum for its 193 Member States to express their views, through the General Assembly, the Security Council, the Economic and Social Council and other bodies and committees. The work of the United Nations reaches every corner of the globe. Although best known for peacekeeping, peacebuilding, conflict prevention and humanitarian assistance, there are many other ways the United Nations and its System (specialized agencies, funds and programmes) affect our lives and make the world a better place. The Organization works on a broad range of fundamental issues, from sustainable development, environment and refugees protection, disaster relief, counter terrorism, disarmament and non-proliferation, to promoting democracy, human rights, gender equality and the advancement of women, governance, economic and social development and international health, clearing landmines, expanding food production, and more, in order to achieve its goals and coordinate efforts for a safer world for this and future generations.
Option B is incorrect because the United Nations was not formed in 1947. The United Nations was formed in 1945.
Option C is incorrect because the United Nations was not formed in 1954. The United Nations was formed in 1945.
Option D is incorrect because the United Nations was not formed in 1919. The United Nations was formed in 1945.