Correct Answer:
D. Rio de Janeiro
The correct answer is Rio de Janeiro. The First United Nations Conference on Environment and Development, famously known as the Earth Summit, was indeed held in Rio de Janeiro, Brazil, in 1992. This landmark event brought together world leaders to address pressing environmental and developmental challenges, leading to significant agreements like Agenda 21, the Rio Declaration, and the Conventions on Biological Diversity and Climate Change. Johannesburg hosted the World Summit on Sustainable Development in 2002, a follow-up to the Earth Summit. Nairobi is home to the UNEP headquarters, while New York often hosts UN General Assembly sessions but not this specific conference.