World Water Day is observed on

The correct answer is B, 5 June. World Environment Day marks the opening of the United Nations Conference on the Human Environment held at Stockholm in 1972, and it has been observed since 1974 under the lead of the United Nations Environment Programme, with a fresh theme and a host country each year. Option A is wrong because 22 April is Earth Day, which began in the United States in 1970 as a citizens' movement and is a different observance altogether. Option C is wrong because 8 June is World Oceans Day, devoted to the seas and to marine life. Option D is wrong because 16 September is World Ozone Day, which marks the signing of the Montreal Protocol on substances that deplete the ozone layer in 1987.

The correct answer is B, the World Health Organization came into being. The constitution of the World Health Organization took effect on 7 April 1948, and the anniversary of that day has been kept as World Health Day since 1950, with a theme chosen by the organisation; its headquarters are at Geneva in Switzerland. Option A is wrong because the Red Cross was founded in the eighteen sixties by Henry Dunant, and the day linked to it is 8 May, his birthday. Option C is wrong because penicillin was discovered by Alexander Fleming in 1928, well before the World Health Organization existed, and no international day marks it. Option D is wrong because Edward Jenner gave the first vaccination against smallpox in 1796, which is not the reason for this date either.

The correct answer is B, Ramsar Convention. The Convention on Wetlands was signed on 2 February 1971 in the Iranian city of Ramsar on the shore of the Caspian Sea, and the wetlands listed under it are still called Ramsar sites; the day has been observed on this date since 1997. Option A is wrong because the Basel Convention deals with the movement of hazardous wastes across borders and was adopted in 1989. Option C is wrong because CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora, was adopted on 3 March 1973 and gives World Wildlife Day its date. Option D is wrong because the text of the Convention on Biological Diversity was adopted on 22 May 1992, which is why the International Day for Biological Diversity falls on that date.

The correct answer is A, 16 September. The day marks the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer on 16 September 1987, an agreement to phase out chlorofluorocarbons and other ozone destroying chemicals, and it is often called the most successful environmental treaty. Option B is wrong because 5 June is World Environment Day, tied to the Stockholm Conference of 1972. Option C is wrong because 23 March is World Meteorological Day, which marks the day in 1950 on which the convention setting up the World Meteorological Organization came into force. Option D is wrong because 22 May is the International Day for Biological Diversity, tied to the adoption of the text of the Convention on Biological Diversity in 1992.

The correct answer is A, 1 December. World AIDS Day has been observed on the first of December since 1988 and was the first global health day of its kind, its symbol being the red ribbon; the theme changes every year and the day is used to press for testing, treatment and an end to stigma. Option B is wrong because 3 December is the International Day of Persons with Disabilities. Option C is wrong because 10 December is Human Rights Day, marking the adoption of the Universal Declaration of Human Rights in 1948. Option D is wrong because 14 November is World Diabetes Day, placed on the birth anniversary of Frederick Banting, one of the discoverers of insulin, and in India the same date is observed as Children's Day.