Kyoto Protocol was endorsed at CoP-3, CoP-5, CoP-6, CoP-4?

The correct option is A CoP-3
The Kyoto Protocol was adopted at the third session of the Conference of Parties to the UNFCCC (COP 3) in 1997 in Kyoto, Japan. The Kyoto Protocol is an international treaty, which extends the 1992 United Nations Framework Convention on Climate Change (UNFCCC) that commits State Parties to reduce greenhouse gases emissions, based on the premise that (a) global warming exists and (b) man-made CO2 emissions have caused it. So, the correct answer is 'CoP-3'