The correct option is A Rio-de-Janeiro
In 1992, the Earth Summit was held at Rio-de-Janeiro at which the leaders of 178 nations gathered to support the idea of the sustainable development. There were the following outcomes of the Earth Summit:
1. Convention on climate change
2. Convention on biodiversity
3. Agenda 21 for sustainable development
The event focussed on narrowing the gap between industrialized and developing economies, poverty, war etc. The idea of the Summit was to maintain the economic and social progress along with the harmony of nature.
Hence, the correct answer is 'Rio-de-Janeiro'