The correct answer is option 4: An average of 5.2% below 1990 levels.

The Kyoto Protocol is an international agreement that aims to address climate change by reducing greenhouse gas emissions. Developed nations, as well as economies in transition, have committed to specific targets for reducing their emissions.

Option 1 states an average of 4% below 1990 levels. This is not correct because the correct answer is 5.2% below 1990 levels.

Option 2 states an average of 5% below 2000 levels. This is not correct because the target is based on 1990 levels, not 2000 levels.

Option 3 states an average of 4.2% below 2000 levels. This is not correct because, again, the target is based on 1990 levels, not 2000 levels.

The Kyoto Protocol requires developed nations and economies in transition to reduce their greenhouse gas emissions by an average of 5.2% below their 1990 levels during the years 2008-2012. This target represents an effort to combat climate change and mitigate its impact on the environment.