The Kyoto Protocol introduced several 'flexibility mechanisms' to help developed countries meet their emission reduction targets. Which mechanism allowed Annex I countries to invest in emission-reducing projects in developing (non-Annex I) countries and receive carbon credits in return?

Explanation

The Clean Development Mechanism (CDM) allowed developed countries (Annex I) to implement emission-reduction projects in developing countries (non-Annex I) and earn certified emission reduction (CER) credits, which could be counted towards meeting their Kyoto targets. Joint Implementation (JI) involved projects between two Annex I countries, while Emissions Trading (ET) allowed Annex I countries to trade emission allowances.