Global warming is already cutting substantially into potential crop yields in some countri

es—to such an extent that it may be a factor in the food price【C1】______ that have caused worldwide stress in recent years, researchers suggest in a new study. Wheat yields in recent years were down by more than 10 percent in Russia and by a few percentage points【C2】______ in India, France and China compared with【C3】______ they probably would have been without rising【C4】______, according to the study. Corn yields were【C5】______ a few percentage points in China, Brazil and France from what would have been【C6】______, said the researchers, whose findings were published in Fridays【C7】______ of the journal Science. Some countries saw small gains from the temperature increases, however. And in all countries, the【C8】______ carbon dioxide that humans are【C9】______ into the air acted as a【C10】______ that encouraged plant growth,【C11】______ some of the losses from rising temperatures caused by that same greenhouse gas. 【C12】______, the studys authors found that when the gains in some countries were weighed【C13】______ the losses in other countries, the overall global【C14】______ of climate change has been small so far: losses of a few percentage points for wheat and corn from what they would have been【C15】______ climate change. The general impact on production of rice and soybeans was【C16】______, with gains in some regions entirely counterbalancing losses in others. 【C17】______ the authors of the study pointed out that temperature increases were expected to【C18】______ in coming decades, making it likely that the challenges【C19】______ food production will grow in a era when demand is expected to【C20】_____ sharply.

【C1】

A．decreases

B．reductions

C．increases

D．additions