Question: What type of vegetation is in the central area of the country Dr. Babatunde Osotimehin is from?

full_context: Document 1: United Nations: The UN has six principal organs: the General Assembly (the main deliberative assembly); the Security Council (for deciding certain resolutions for peace and security); the Economic and Social Council (ECOSOC; for promoting international economic and social co-operation and development); the Secretariat (for providing studies, information, and facilities needed by the UN); the International Court of Justice (the primary judicial organ); and the UN Trusteeship Council (inactive since 1994). UN System agencies include the World Bank Group, the World Health Organization, the World Food Programme, UNESCO, and UNICEF. The UN's most prominent officer is the Secretary - General, an office held by Portuguese António Guterres since 2017. Non-governmental organizations may be granted consultative status with ECOSOC and other agencies to participate in the UN's work.
Document 2: United Nations Monitoring, Verification and Inspection Commission: In 2000, the Secretary-General of the United Nations appointed Dr. Hans Blix of Sweden to be the Commission's Executive Chairman. He served from 1 March 2000 until the end of June 2003, roughly 3 months after Iraq had been invaded.
Document 3: United Nations Population Fund: UNFPA began operations in 1969 as the United Nations Fund for Population Activities (the name was changed in 1987) under the administration of the United Nations Development Fund. In 1971 it was placed under the authority of the United Nations General Assembly.
Document 4: United Nations: The UN has six principal organs: the General Assembly (the main deliberative assembly); the Security Council (for deciding certain resolutions for peace and security); the Economic and Social Council (ECOSOC; for promoting international economic and social co-operation and development); the Secretariat (for providing studies, information, and facilities needed by the UN); the International Court of Justice (the primary judicial organ); and the UN Trusteeship Council (inactive since 1994). UN System agencies include the World Bank Group, the World Health Organization, the World Food Programme, UNESCO, and UNICEF. The UN's most prominent officer is the Secretary - General, an office held by Portuguese politician and diplomat António Guterres since 2017. Non-governmental organizations may be granted consultative status with ECOSOC and other agencies to participate in the UN's work.
Document 5: United Nations Population Fund: The UNFPA supports programs in more than 150 countries, territories and areas spread across four geographic regions: Arab States and Europe, Asia and the Pacific, Latin America and the Caribbean, and sub-Saharan Africa. Around three quarters of the staff work in the field. It is a member of the United Nations Development Group and part of its Executive Committee.
Document 6: Geography of Nigeria: With the Intertropical Convergence Zone (ITCZ) swinging northward over West Africa from the Southern Hemisphere in April, heavy showers coming from pre-monsoonal convective clouds mainly in the form of squall lines also known as the north easterlies formed mainly as a result of the interactions of the two dominant airmasses in Nigeria known as the Maritime tropical (south westerlies) and the Continental tropical (north easterlies), begins in central Nigeria while the Monsoons from the south atlantic ocean arrives in central Nigeria in July bringing with it high humidity, heavy cloud cover and heavy rainfall which can be daily occurrence lasting till September when the monsoons gradually begin retreating southward to the southern part of Nigeria. Rainfall totals in central Nigeria varies from 1,100 mm (43.3 in) in the lowlands of the river Niger Benue trough to over 2,000 mm (78.7 in) along the south western escarpment of the Jos Plateau.
Document 7: John Hendra: Prior to this position he served from 2011-2014 as UN Assistant Secretary-General and Deputy Executive Director, Policy and Programme, at the United Nations Entity for Gender Equality and the Empowerment of Women (UN Women). He was appointed by the United Nations Secretary-General Ban Ki-Moon on 11 March 2011. John has also been closely involved in the process of formulating the 2030 Agenda, including as a member of the Informal Senior Coordination Group (2012-2014) and as Co-Chair of the UN Development Group's MDG Task Force. He also recently served as Co-Chair of the UN Leadership Group.
Document 8: Sahara: To the south, the Sahara is bounded by the Sahel, a belt of dry tropical savanna with a summer rainy season that extends across Africa from east to west. The southern limit of the Sahara is indicated botanically by the southern limit of Cornulaca monacantha (a drought-tolerant member of the Chenopodiaceae), or northern limit of Cenchrus biflorus, a grass typical of the Sahel. According to climatic criteria, the southern limit of the Sahara corresponds to the 150 mm (5.9 in) isohyet of annual precipitation (this is a long-term average, since precipitation varies annually).
Document 9: Nafis Sadik: Nafis Sadik (born 1929), currently Special Adviser to the UN Secretary General with additional responsibilities as Special Envoy for HIV/AIDS in Asia, and former executive director of the United Nations Population Fund (UNFPA) from 1987 to 2000. She retired from this job in December 2000.
Document 10: Chad: Chad has several regions: a desert zone in the north, an arid Sahelian belt in the centre and a more fertile Sudanian Savanna zone in the south. Lake Chad, after which the country is named, is the largest wetland in Chad and the second - largest in Africa. The capital N'Djamena is the largest city.
Document 11: Sahara: To the north, the Sahara skirts the Mediterranean Sea in Egypt and portions of Libya, but in Cyrenaica and the Maghreb, the Sahara borders the Mediterranean forest, woodland, and scrub ecoregions of northern Africa, all of which have a Mediterranean climate characterized by hot summers and cool and rainy winters. According to the botanical criteria of Frank White and geographer Robert Capot-Rey, the northern limit of the Sahara corresponds to the northern limit of date palm cultivation and the southern limit of the range of esparto, a grass typical of the Mediterranean climate portion of the Maghreb and Iberia. The northern limit also corresponds to the 100 mm (3.9 in) isohyet of annual precipitation.
Document 12: Nigeria: Everything in between the far south and the far north is savannah (insignificant tree cover, with grasses and flowers located between trees). Rainfall is more limited, to between 500 and 1,500 millimetres (20 and 60 in) per year. The savannah zone's three categories are Guinean forest-savanna mosaic, Sudan savannah, and Sahel savannah. Guinean forest-savanna mosaic is plains of tall grass interrupted by trees. Sudan savannah is similar but with shorter grasses and shorter trees. Sahel savannah consists of patches of grass and sand, found in the northeast. In the Sahel region, rain is less than 500 millimetres (20 in) per year and the Sahara Desert is encroaching. In the dry north-east corner of the country lies Lake Chad, which Nigeria shares with Niger, Chad and Cameroon.
Document 13: United Nations Population Fund: Executive Directors and Under-Secretaries General of the UN
2011–present Dr Babatunde Osotimehin (Nigeria)
2000–2010 Ms Thoraya Ahmed Obaid (Saudi Arabia)
1987–2000 Dr Nafis Sadik (Pakistan)
1969–87 Mr Rafael M. Salas (Philippines)
Document 14: Geography of Nigeria: Nigeria, like the rest of West Africa and other tropical lands, has only two seasons. These are the dry season and the rainy season. The dry season is accompanied by a dust laden airmass from the Sahara Desert, locally known as Harmattan, or by its main name, The Tropical Continental (CT) airmass, while the rainy season is heavily influenced by an airmass originating from the south atlantic ocean, locally known as the south west wind, or by its main name, The Tropical Maritime (MT) airmass. These two major wind systems in Nigeria are known as the trade winds.
Document 15: Sahara: The desert comprises much of North Africa, excluding the fertile region on the Mediterranean Sea coast, the Atlas Mountains of the Maghreb, and the Nile Valley in Egypt and Sudan. It stretches from the Red Sea in the east and the Mediterranean in the north to the Atlantic Ocean in the west, where the landscape gradually changes from desert to coastal plains. To the south, it is bounded by the Sahel, a belt of semi-arid tropical savanna around the Niger River valley and the Sudan Region of Sub-Saharan Africa.
ground_truth: savannah
sub_queries: Dr Babatunde Osotimehin hailed from what country? Answer: Nigeria
What type of vegetation is in central Nigeria ? Answer: savannah