Four decades ago a group of college students visited the mountains of Borneo to examine moth   populations. Now a team of British scientists, including a member of the original trip, has returned to the same sites to repeat the survey. They have found that, due to rising temperatures, the insects now live 68 meters higher. Global warming is forcing tropical   species uphill to escape the rising temperatures at a rate of nearly 2 meters a year, the new study from Borneo suggests. Since this was the only chance to repeat the original survey, the scientist did everything they could to do it exactly the same way, going at the same time of year, in July and August, using photographs to find the exact original sites of the moth traps. "While this is the first study of insects, a few other studies of tropical species are starting to appear," said Thomas. "If you look across all those studies, you'll find the same results, and it's extremely difficult to think of any other explanation for them." While some species might survive by finding places on the mountains with temperatures similar to those of their original habitats, others may run out of habitat on the rocky peaks, warns the study. In a paper in the journal Naturein 2004, Thomas and 13 other experts analyzed the habitats of 1,100 species on five continents, and estimated that on average one quarter were at risk of extinction. Last year a paper published in the Public Library of Science in the US warned that the risk of extinction in the tropics was becoming more and more serious. The authors, Jana and Steven Vamosi, estimated that 20-45% of tropical species were at risk of extinction. We can learn from the passage that   _  .
this survey of moths has been carried out many times some scientists have put forward other explanations for the results scientists tried to repeat the original survey 20-45% of tropical species were estimated to be at risk of extinction in 2004
Question: Four decades ago a group of college students visited the mountains of Borneo to examine moth   populations. Now a team of British scientists, including a member of the original trip, has returned to the same sites to repeat the survey. They have found that, due to rising temperatures, the insects now live 68 meters higher. Global warming is forcing tropical   species uphill to escape the rising temperatures at a rate of nearly 2 meters a year, the new study from Borneo suggests. Since this was the only chance to repeat the original survey, the scientist did everything they could to do it exactly the same way, going at the same time of year, in July and August, using photographs to find the exact original sites of the moth traps. "While this is the first study of insects, a few other studies of tropical species are starting to appear," said Thomas. "If you look across all those studies, you'll find the same results, and it's extremely difficult to think of any other explanation for them." While some species might survive by finding places on the mountains with temperatures similar to those of their original habitats, others may run out of habitat on the rocky peaks, warns the study. In a paper in the journal Naturein 2004, Thomas and 13 other experts analyzed the habitats of 1,100 species on five continents, and estimated that on average one quarter were at risk of extinction. Last year a paper published in the Public Library of Science in the US warned that the risk of extinction in the tropics was becoming more and more serious. The authors, Jana and Steven Vamosi, estimated that 20-45% of tropical species were at risk of extinction. We can learn from the passage that   _  .
A. this survey of moths has been carried out many times
B. some scientists have put forward other explanations for the results
C. scientists tried to repeat the original survey
D. 20-45% of tropical species were estimated to be at risk of extinction in 2004
Answer: