The first Earth summit was held at :

The correct answer is: B. Rio De Janeiro

The United Nations Conference on Environment and Development (UNCED), also known as the Earth Summit, was a major United Nations conference held in Rio de Janeiro from 3 to 14 June 1992. The summit was attended by more than 178 governments and 1,400 non-governmental organizations (NGOs). The main outcome of the summit was the Rio Declaration on Environment and Development, which set out 27 principles for sustainable development. The summit also produced Agenda 21, a comprehensive plan of action for sustainable development in the 21st century.

Buenos Aires is the capital and most populous city of Argentina. It is located on the western shore of the Río de la Plata, on the South Atlantic coast. Buenos Aires is the second-largest city in South America after São Paulo, Brazil. The city is home to the National Congress of Argentina, the Casa Rosada presidential palace, and the Metropolitan Cathedral of Buenos Aires. Buenos Aires is a major center for culture, education, and finance.

Dar es Salaam is the largest city and the former capital of Tanzania. It is located on the coast of the Indian Ocean, at the mouth of the Rufiji River. Dar es Salaam is a major port city and a center for trade and commerce. The city is also home to a number of universities and other educational institutions.

None of these is the correct answer.