Under the Kyoto Protocol, developed countries took on a bigger share of limits, which led to

positive changes in the pollution levels worldwide.

increases in the participation of developing countries.

China becoming the leading producer of carbon dioxide emissions.

Canada becoming the world leader in its lowered levels of pollution.

The third choice is best, which states that China became the leading CO2 emitter. This is because China was considered an emerging economy, and so the restrictions on it were not as heavy. In fact, many of the developed countries decided to export a lot of their heavy industries and manufacturing operations to China, thus causing larger industrial emissions from China while lowering those in their own countries.