The correct answer is option 'D' - South America. South America has the highest percentage of forest cover compared to Africa, Asia, and North America. This can be attributed to several factors including the region's geographical characteristics and government policies.

1. Geographical Factors:
South America is home to the Amazon rainforest, which is the largest tropical rainforest in the world. It spans across several countries including Brazil, Peru, Colombia, and Venezuela. The Amazon rainforest alone accounts for a significant portion of South America's forest cover. Its vast size and dense vegetation contribute to the overall high percentage of forest cover in the region.

2. Biodiversity:
South America is known for its incredible biodiversity, with numerous species of plants and animals residing within its forests. The rich biodiversity of the region attracts attention and efforts for conservation, leading to a higher priority placed on maintaining forest cover. Conservation efforts and protected areas help ensure the preservation of South America's forests.

3. Government Policies:
Several South American countries have implemented policies to protect and preserve their forest resources. For example, Brazil has established the Legal Amazon, an area covering nine states with strict regulations on deforestation. Additionally, countries like Peru and Colombia have made efforts to combat illegal logging and promote sustainable forest management. These policies have contributed to the maintenance of high forest cover in South America.

4. International Awareness:
The importance of the Amazon rainforest and other South American forests in regulating global climate and supporting biodiversity has gained international attention. Efforts by global organizations, environmental activists, and scientists have raised awareness about the need to protect these forests. This increased awareness has resulted in more funds and initiatives dedicated to forest conservation in South America.

In conclusion, the percentage of forest cover is highest in South America due to geographical factors, rich biodiversity, government policies, and international awareness. The presence of the Amazon rainforest, along with efforts to protect and preserve forests, has contributed to the region's high forest cover.