Large areas of the Amazon rainforest were grassland until just 2,000 years ago when it has been found. Researchers say the find gives new light on the Amazon's history - and show it was a savannah   rather than the high forest it is today. They believe much of the area was grassland until a natural shift to a wetter climate about 2,000 years ago let the rainforests form, according to a study that challenges common belief that the world's biggest tropical forest is far older. The arrival of European diseases after Columbus crossed the Atlantic in 1492 may also have sped up the growth of forests by killing the local people farming the region, the scientists wrote in the US journal Proceedings of the National Academy of Sciences (PNAS).  "The dominant ecosystem was more like a savannah than the rainforest we see today," John Carson, lead author at the University of Reading in England, said of the findings about the southern Amazon. The scientists said that a shift toward wetter conditions, perhaps caused by natural shifts in the Earth's orbit around the sun, led to growth of more trees starting about 2,000 years ago. The "findings suggest that rather than being rainforest hunter-gatherers, or large-scale forest clearers, the people of the Amazon from 2,500 to 500 years ago were farmers," the University of Reading said in a statement. Carson said that perhaps a fifth of the Amazon basin, in the south, may have been savannah until the shift, with forests covering the rest. In one lake, Laguna Granja, rainforest plants only took over from grass as the main sources of sediments   about 500 years old, suggesting a link to the arrival of Europeans. And understanding the forest could help solve puzzles about climate change. The Amazon rainforest affects climate change because trees soak up heat-trapping carbon dioxide as they grow and release it when they rot or are burnt. Brazil has sharply slowed deforestation   rates in recent years. Brazil slows deforestation rate because Brazil     .
wants to have more land for farming intends to help prevent global warming wants to turn the rainforest into savannah attempts to understand what causes climate change
Question: Large areas of the Amazon rainforest were grassland until just 2,000 years ago when it has been found. Researchers say the find gives new light on the Amazon's history - and show it was a savannah   rather than the high forest it is today. They believe much of the area was grassland until a natural shift to a wetter climate about 2,000 years ago let the rainforests form, according to a study that challenges common belief that the world's biggest tropical forest is far older. The arrival of European diseases after Columbus crossed the Atlantic in 1492 may also have sped up the growth of forests by killing the local people farming the region, the scientists wrote in the US journal Proceedings of the National Academy of Sciences (PNAS).  "The dominant ecosystem was more like a savannah than the rainforest we see today," John Carson, lead author at the University of Reading in England, said of the findings about the southern Amazon. The scientists said that a shift toward wetter conditions, perhaps caused by natural shifts in the Earth's orbit around the sun, led to growth of more trees starting about 2,000 years ago. The "findings suggest that rather than being rainforest hunter-gatherers, or large-scale forest clearers, the people of the Amazon from 2,500 to 500 years ago were farmers," the University of Reading said in a statement. Carson said that perhaps a fifth of the Amazon basin, in the south, may have been savannah until the shift, with forests covering the rest. In one lake, Laguna Granja, rainforest plants only took over from grass as the main sources of sediments   about 500 years old, suggesting a link to the arrival of Europeans. And understanding the forest could help solve puzzles about climate change. The Amazon rainforest affects climate change because trees soak up heat-trapping carbon dioxide as they grow and release it when they rot or are burnt. Brazil has sharply slowed deforestation   rates in recent years. Brazil slows deforestation rate because Brazil     .
A. wants to have more land for farming
B. intends to help prevent global warming
C. wants to turn the rainforest into savannah
D. attempts to understand what causes climate change
Answer: