题目

阅读下列短文, 从给的四个选项 (A、B、C和D) 中, 选出最佳选项。 “Plants were expected to get larger with increased carbon dioxide in atmosphere, but changes in temperature, humidity and nutrient availability seem to trumped the benefits of increased carbon dioxide，” said researchers from the National University of Singapore. 45 percent of the species studied now reach smaller adult sizes than they did in the past. The researchers pointed out that warmer temperatures and changing habitats, caused by climate change, are possible reasons for shrinking creatures. They had no sooner arrived at the airport       it was time to check in.A．whenB．beforeC．thanD．though