The correct answer is: D. International Human Solidarity Day
International Human Solidarity Day is observed on 31 May every year. It was proclaimed by the United Nations General Assembly in 2005 to promote understanding, tolerance, and solidarity among peoples and nations. The day also aims to highlight the importance of international cooperation in addressing global challenges.
World day for War Orphans is observed on 6 June every year. It was established by the United Nations General Assembly in 2002 to raise awareness of the plight of war orphans and to promote their rights and well-being.
United Nations Day for South-South Cooperation is observed on 12 September every year. It was established by the United Nations General Assembly in 1986 to promote South-South cooperation, which is cooperation among developing countries.
World No Tobacco Day is observed on 31 May every year. It was established by the World Health Organization in 1987 to raise awareness of the dangers of tobacco use and to encourage people to quit smoking.