Plants are flowering faster than scientists predicted  in reaction to climate change,which could have long damaging effects on food chains and ecosystems. Global warming is having a great effect on hundreds of plant and animal species around the world,changing some living patterns,scientists say. Increased carbon dioxide (CO2)in the air from burning coal and oil can have an effect on how plants produce oxygen,while higher temperatures and changeable rainfall patterns can change their patterns of growth. "Predicting species' reaction to climate change is a major challenge in ecology,"said the researchers of several U.S. universities.They said plants had been the key object of study because their reaction to climate change could have an effect on food chains and ecosystem services. The study,published on the Nature website,uses the findings from plant life cycle studies and experiments across four continents and 1,634 species.It found that some experiments had underestimated  the speed of flowering by 8.5 times and leafing by 4 times. "Across all species,the experiments under-predicted the speed of the advance--for both leafing and flowering -- that results from temperature increases,"the study said. The design of future experiments may need to be improved to better predict how plants will react to climate change,it said. Plants are necessary for life on the Earth.They are the base of the food chain,using photosynthesis  to produce sugar from carbon dioxide and water.They let out oxygen which is needed by nearly every organism on the planet. Scientists believe the world's average temperature has risen by about 0.8 degC since 1900,and nearly 0.2 degC every ten years since 1979. So far,efforts to cut emissions   of planet-warming greenhouse gases are not seen as enough to prevent the Earth heating up beyond 2 degC this century-- a point scientists say will bring the danger of a changeable climate in which weather extremes are common,leading to drought,floods,crop failures and rising sea levels. Scientists pay special attention to the study of plants because   .
they can prove the climate change clearly they are very important in the food chains they play a leading role in reducing global warming they are growing and flowering much faster than before
Question: Plants are flowering faster than scientists predicted  in reaction to climate change,which could have long damaging effects on food chains and ecosystems. Global warming is having a great effect on hundreds of plant and animal species around the world,changing some living patterns,scientists say. Increased carbon dioxide (CO2)in the air from burning coal and oil can have an effect on how plants produce oxygen,while higher temperatures and changeable rainfall patterns can change their patterns of growth. "Predicting species' reaction to climate change is a major challenge in ecology,"said the researchers of several U.S. universities.They said plants had been the key object of study because their reaction to climate change could have an effect on food chains and ecosystem services. The study,published on the Nature website,uses the findings from plant life cycle studies and experiments across four continents and 1,634 species.It found that some experiments had underestimated  the speed of flowering by 8.5 times and leafing by 4 times. "Across all species,the experiments under-predicted the speed of the advance--for both leafing and flowering -- that results from temperature increases,"the study said. The design of future experiments may need to be improved to better predict how plants will react to climate change,it said. Plants are necessary for life on the Earth.They are the base of the food chain,using photosynthesis  to produce sugar from carbon dioxide and water.They let out oxygen which is needed by nearly every organism on the planet. Scientists believe the world's average temperature has risen by about 0.8 degC since 1900,and nearly 0.2 degC every ten years since 1979. So far,efforts to cut emissions   of planet-warming greenhouse gases are not seen as enough to prevent the Earth heating up beyond 2 degC this century-- a point scientists say will bring the danger of a changeable climate in which weather extremes are common,leading to drought,floods,crop failures and rising sea levels. Scientists pay special attention to the study of plants because   .
A. they can prove the climate change clearly
B. they are very important in the food chains
C. they play a leading role in reducing global warming
D. they are growing and flowering much faster than before
Answer: