Question: Who explored the mainland of the continent on which the river that the Tebicuary River is a tributary of is located?

full_context: Document 1: Quiquibey River: The Quiquibey River is a river in the Pilón Lajas Biosphere Reserve and Communal Lands in the north of Bolivia. The Quiquibey River joins the Beni River south of Rurrenabaque (upstream and south of Beni's tributary the Tuichi River). The river is the border between the departments of Beni and La Paz.
Document 2: Juruá River: The Juruá River (Portuguese "Rio Juruá"; Spanish "Río Yurúa") is a southern affluent river of the Amazon River west of the Purus River, sharing with this the bottom of the immense inland Amazon depression, and having all the characteristics of the Purus as regards curvature, sluggishness and general features of the low, half-flooded forest country it traverses.
Document 3: Guaíra, Paraná: Guaíra is a municipality in the state of Paraná in the Southern Region of Brazil. The population is 32,591 (2015 est.) in an area of 560 km². The elevation is 517 m. This place name comes from the Tupi language and means "place difficult to access". The city is served by Guaíra Airport.
Document 4: Puerto Rico: Originally populated by the indigenous Taíno people, the island was claimed in 1493 by Christopher Columbus for Spain during his second voyage. Later it endured invasion attempts from the French, Dutch, and British. Four centuries of Spanish colonial government influenced the island's cultural landscapes with waves of African slaves, Canarian, and Andalusian settlers. In the Spanish Empire, Puerto Rico played a secondary, but strategic role when compared to wealthier colonies like Peru and the mainland parts of New Spain. Spain's distant administrative control continued up to the end of the 19th century, helping to produce a distinctive creole Hispanic culture and language that combined elements from the Native Americans, Africans, and Iberians. In 1898, following the Spanish -- American War, the United States acquired Puerto Rico under the terms of the Treaty of Paris.
Document 5: Tebicuary River: The Tebicuary River (Spanish: Río Tebicuary), a tributary of Paraguay River is a river in Paraguay. Located in the southwestern part of that country, it flows eastwards discharging to Paraguay River about 45 km south of Formosa and 30 km north of Pilar.
Document 6: History of South America: The Spanish colonies won their independence in the first quarter of the 19th century, in the Spanish American wars of independence. Simón Bolívar (Greater Colombia, Peru, Bolivia), José de San Martín (United Provinces of the River Plate, Chile, and Peru), and Bernardo O'Higgins (Chile) led their independence struggle. Although Bolivar attempted to keep the Spanish - speaking parts of the continent politically unified, they rapidly became independent of one another.
Document 7: Guaporé River: Guaporé River (Portuguese: Rio Guaporé) is a river in western Brazil and northeastern Bolivia. Its Bolivian name is Río Iténez. It is 1,530 km (950 mi) long; 970 km (600 mi) of the river forms the border between Brazil and Bolivia.
Document 8: San Ignacio de Loyola International Bridge: The San Ignacio de Loyola International Bridge (Spanish: Puente Internacional San Ignacio de Loyola) is a road bridge that crosses the border between Argentina and Paraguay over the Pilcomayo River, from the Argentine city of Clorinda, to José Falcón, near Asunción, Paraguay's capital.
Document 9: Black people: Approximately 12 million Africans were shipped to the Americas during the Atlantic slave trade from 1492 to 1888, with 11.5 million of those shipped to South America and the Caribbean. Brazil was the largest importer in the Americas, with 5.5 million African slaves imported, followed by the British Caribbean with 2.76 million, the Spanish Caribbean and Spanish Mainland with 1.59 million Africans, and the French Caribbean with 1.32 million. Today their descendants number approximately 150 million in South America and the Caribbean. In addition to skin color, other physical characteristics such as facial features and hair texture are often variously used in classifying peoples as black in South America and the Caribbean. In South America and the Caribbean, classification as black is also closely tied to social status and socioeconomic variables, especially in light of social conceptions of "blanqueamiento" (racial whitening) and related concepts.
Document 10: Languages of South America: Spanish is the majority language of South America, by a small margin. Portuguese, with slightly fewer speakers than Spanish, is the second most spoken language on the continent.
Document 11: Paraguay: Paraguay (; ; , ), officially the Republic of Paraguay (; ), is a country in South America. It is bordered by Argentina to the south and southwest, Brazil to the east and northeast, and Bolivia to the northwest. Although it is one of only two landlocked countries in South America (the other is Bolivia), the country has coasts, beaches and ports on the Paraguay and Paraná rivers that give exit to the Atlantic Ocean through the . Due to its central location in South America, it is sometimes referred to as "Corazón de Sudamérica" ("Heart of South America").
Document 12: São Lourenço River (Mato Grosso): The São Lourenço River is a tributary of the Paraguay River within the Pantanal, an alluvial plain that spans portions of Brazil, Bolivia and Paraguay.
Document 13: Bermejo River: The Bermejo River (Spanish, Río Bermejo) is a river in South America that flows from Bolivia to the Paraguay River in Argentina. The river is generally called Bermejo in spite of its different names along its way, but it also has its own Native American names; in Wichí it is called Teuco, and in Guaraní it is called Ypitá. In the plains of Argentina's Gran Chaco the Bermejo forms wetlands and splits into two branches. The southern branch is the bed of the old Bermejo River, now an intermittent stream called Río Bermejito. The northern branch is now the main stem of the Bermejo and is called the Teuco River ("Río Teuco"), Bermejo Nuevo, or simply the Bermejo River. The two branches rejoin at , near Villa Río Bermejito, forming the Lower Bermejo River.
Document 14: Paraguay River: The Paraguay River (Río Paraguay in Spanish, Rio Paraguai in Portuguese, Ysyry Paraguái in Guarani) is a major river in south-central South America, running through Brazil, Bolivia, Paraguay and Argentina. It flows about from its headwaters in the Brazilian state of Mato Grosso to its confluence with the Paraná River north of Corrientes and Resistencia.
Document 15: South America: The continent's cultural and ethnic outlook has its origin with the interaction of indigenous peoples with European conquerors and immigrants and, more locally, with African slaves. Given a long history of colonialism, the overwhelming majority of South Americans speak Portuguese or Spanish, and societies and states commonly reflect Western traditions.
ground_truth: European conquerors
sub_queries: What is Tebicuary River a tributary of? Answer: Paraguay River
Which continent is Paraguay River on? Answer: South America
who explored the main land of South America Answer: European conquerors