The Intergovernmental Panel on Climate Change (IPCC) was set up in 1988 to assess information on climate change and its impact. Its Third Assessment Report predicts global temperature rises by 2100 of between 1.4°C and 5.8°C. Although the issue of the changing climate is very complex and some changes are uncertain, temperature rises are expected to affect countries throughout the world and have a knock-on effect with sea-level rises.Scientists have argued about whether temperature rises are due to human activities or due to natural changes in our environment. The IPCC announced in 2001 that "most of the warming observed over the last 50 years is likely to be attributable to human activities". This was a more forceful statement than in 1996 when the Second Assessment Report stated that there was a "discernible human influence on the climate" which was the first time they had concluded such a link. Many experts believe the faster the climate changes, the greater the risk will be.Key points of the projections for climate change globally include that by the second half of the 21st century, wintertime rainfall in the northern mid to high latitudes and Antarctica will rise, that meanwhile Australia, Central America and southern Africa are likely to see decreases in autumn precipitation, that some land areas in the tropics will see more rainfall, and that there will generally be more hot days over land areas.
The IPCC announcement three years ago that "most of the warming observed over the last 50 years is"________.
A．possibly due to human activities
B．possibly because human activities
C．due to likely human activities
D．human activities likely attributable