The correct answer is option 3, which states that both 1 and 2 are correct. Let`s dissect each option to understand why governments find it difficult to agree on ways to limit greenhouse gas emissions.

Option 1: "They fear that measures to reduce greenhouse gas emissions will have negative effects on their economy." This option highlights the concern of governments that taking actions to reduce greenhouse gas emissions will have a negative impact on their economies. Some countries heavily depend on industries that produce greenhouse gases, such as fossil fuel industries, and implementing measures to reduce emissions may result in a loss of jobs and economic slowdown.

Option 2: "The developing nations regard mandatory limits on their emissions as attempts by the richer countries to hobble their progress." This option acknowledges the perspective of developing nations that see mandatory limits on their emissions as unfair and limiting their ability to develop and catch up economically with richer nations. They argue that richer countries have historically emitted more greenhouse gases and should take the lead in reducing emissions.

Therefore, it is the combination of these two factors - economic concerns for some countries and the perception of unfairness for developing nations - that make it difficult for governments to agree on ways and means to limit greenhouse gas emissions.