Question: Who began exploring the Atlantic coast of the continent where the river that serves as drainage for the southwest plain of the Congo is located?

full_context: Document 1: Yumbi: Yumbi is a town and territory in Plateaux District of Bandundu Province in the Democratic Republic of the Congo. It lies on the eastern bank of the Congo River between Bolobo and Lukolela.
Document 2: Universities' Mission to Central Africa: To advance these goals, it sought to send a mission led by a bishop into Central Africa; Charles Mackenzie was duly consecrated in 1860 and led an expedition in 1861 up the Zambezi into the Shire Highlands. This first expedition was more or less disastrous. The area chosen as a base, near Lake Nyasa (Lake Malawi), proved highly malarial; Bishop Mackenzie died there of the disease on 31 January 1862, along with many local people and three others among the tiny missionary party. Early conversion efforts from this base yielded little result, and supplies ran out or were destroyed during a period of famine. The mission then withdrew from the area, abandoning the graves of the missionaries who had died there, and though it established a new presence in Zanzibar many years passed before it returned to Malawi. Bishop Tozer, Mackenzie's successor, deemed the mission's early years ``a miserable failure ''.
Document 3: Mayombe: Mayombe (or Mayumbe) is a geographic area on the western coast of Africa occupied by low mountains extending from the mouth of the Congo River in the south to the Kouilou-Niari River to the north. The area includes parts of the Democratic Republic of the Congo, Angola (Cabinda Province), the Republic of the Congo and Gabon.
Document 4: Congo River: Railways now bypass the three major falls, and much of the trade of Central Africa passes along the river, including copper, palm oil (as kernels), sugar, coffee, and cotton. The river is also potentially valuable for hydroelectric power, and the Inga Dams below Pool Malebo are first to exploit the Congo river.
Document 5: Geography of Angola: Angola is located on the western Atlantic Coast of Central Africa between Namibia and the Republic of the Congo. It also is bordered by the Democratic Republic of the Congo and Zambia to the east. The country consists of a sparsely watered and somewhat sterile coastal plain extending inland for a distance varying from . Slightly inland and parallel to the coast is a belt of hills and mountains and behind those a large plateau. The total land size is . It has an Exclusive Economic Zone of .
Document 6: Mitumba Mountains: The Mitumba Mountain range stretches along the Western Rift Valley in Eastern Congo (DRC), west of lake Tanganyika. The two main peaks, Mount Kahuzi (3,308 m) and Mount Biéga (2,790 m) are extinct volcanoes.
Document 7: Republic of the Congo: Congo is located in the central-western part of sub-Saharan Africa, along the Equator, lying between latitudes 4°N and 5°S, and longitudes 11° and 19°E. To the south and east of it is the Democratic Republic of Congo. It is also bounded by Gabon to the west, Cameroon and the Central African Republic to the north, and Cabinda (Angola) to the southwest. It has a short coast on the Atlantic Ocean.
Document 8: Livingstone Memorial: The Livingstone Memorial built in 1899 marks the spot where missionary explorer David Livingstone died on 1 May 1873 in Chief Chitambo's village at Ilala near the edge of the Bangweulu Swamps in Zambia. His heart was buried there under a mpundu (also called mvula) tree by his loyal attendants Chuma, Suza Mniasere and Vchopere, before they departed for the coast carrying his body. In their party was an Indian-educated African man named Jacob Wainwright who carved the inscription "LIVINGSTONE MAY 4 1873" and the names of the attendants on the tree.
Document 9: Republic of the Congo: Since the country is located on the Equator, the climate is consistent year-round, with the average day temperature being a humid 24 °C (75 °F) and nights generally between 16 °C (61 °F) and 21 °C (70 °F). The average yearly rainfall ranges from 1,100 millimetres (43 in) in south in the Niari Valley to over 2,000 millimetres (79 in) in central parts of the country. The dry season is from June to August while in the majority of the country the wet season has two rainfall maxima: one in March–May and another in September–November.
Document 10: Republic of the Congo: The Portuguese explorer Diogo Cão reached the mouth of the Congo in 1484. Commercial relationships quickly grew between the inland Bantu kingdoms and European merchants who traded various commodities, manufactured goods, and people captured from the hinterlands. After centuries as a major hub for transatlantic trade, direct European colonization of the Congo river delta began in the late 19th century, subsequently eroding the power of the Bantu societies in the region.
Document 11: Republic of the Congo: The southwest of the country is a coastal plain for which the primary drainage is the Kouilou-Niari River; the interior of the country consists of a central plateau between two basins to the south and north. Forests are under increasing exploitation pressure.
Document 12: Republic of the Congo: The Republic of the Congo's sparse population is concentrated in the southwestern portion of the country, leaving the vast areas of tropical jungle in the north virtually uninhabited. Thus, Congo is one of the most urbanized countries in Africa, with 70% of its total population living in a few urban areas, namely in Brazzaville, Pointe-Noire or one of the small cities or villages lining the 534-kilometre (332 mi) railway which connects the two cities. In rural areas, industrial and commercial activity has declined rapidly in recent years, leaving rural economies dependent on the government for support and subsistence.
Document 13: European exploration of Africa: Henry Morton Stanley, who had in 1871 succeeded in finding and succouring Livingstone (originating the famous line ``Dr. Livingstone, I presume ''), started again for Zanzibar in 1874. In one of the most memorable of all exploring expeditions in Africa, Stanley circumnavigated Victoria Nyanza (Lake Victoria) and Lake Tanganyika. Striking farther inland to the Lualaba, he followed that river down to the Atlantic Ocean -- which he reached in August 1877 -- and proved it to be the Congo.
Document 14: Republic of the Congo: The Republic of the Congo (French: République du Congo), also known as Congo, Congo Republic, West Congo[citation needed], or Congo-Brazzaville, is a country located in Central Africa. It is bordered by five countries: Gabon to the west; Cameroon to the northwest; the Central African Republic to the northeast; the Democratic Republic of the Congo to the east and south; and the Angolan exclave of Cabinda to the southwest.
Document 15: European exploration of Africa: European exploration of Sub-Saharan Africa begins with the Age of Discovery in the 15th century, pioneered by Portugal under Henry the Navigator. The Cape of Good Hope was first reached by Bartolomeu Dias on 12 March 1488, opening the important sea route to India and the Far East, but European exploration of Africa itself remained very limited during the 16th and 17th centuries. The European powers were content to establish trading posts along the coast while they were actively exploring and colonizing the New World. Exploration of the interior of Africa was thus mostly left to the Arab slave traders, who in tandem with the Muslim conquest of the Sudan established far - reaching networks and supported the economy of a number of Sahelian kingdoms during the 15th to 18th centuries.
ground_truth: Henry Morton Stanley
sub_queries: Which river serves as drainage for the southwest plain of the Congo? Answer: Kouilou-Niari River
Kouilou-Niari River >> continent Answer: Africa
who began exploration of Africa 's atlantic coast Answer: Henry Morton Stanley