The correct answer is D. 2%.
A 2% regulation is considered best because it is the most stringent regulation that is still likely to be implemented. A 50% regulation would be very difficult to implement, and a 10% regulation would not be as effective in reducing pollution.
A 2% regulation would require companies to reduce their emissions by 2% each year. This would be a significant reduction, but it would be achievable. Companies would need to invest in new technologies and make changes to their operations, but it would be possible.
A 50% regulation would be much more difficult to implement. Companies would need to make much more significant changes to their operations, and it is not clear that they would be able to do so. This could lead to job losses and other economic problems.
A 10% regulation would not be as effective in reducing pollution. Companies would not need to make as significant changes to their operations, and the reduction in emissions would be smaller. This would not be enough to address the problem of climate change.
Therefore, a 2% regulation is the best option. It is the most stringent regulation that is still likely to be implemented. It would be a significant reduction in emissions, and it would be achievable.