单选题 Some doomsayers are warning that long-range warming or cooling trends in weather patterns will drastically reduce grain production. More optimistic reports, however, point out that, even if such drifts in average temperature do occur, we should expect little change in grain production because there is little evidence that changes in rainfall patterns will occur. Moreover, for most crops, climate-induced yield trends will be masked by both the year-to-year fluctuation of yields and by the enhancement of yields because of technological factors. Which of the following is an assumption on which the more optimistic reports mentioned in the passage are based?

A、 Long-range changes in weather patterns cannot be accurately predicted.
B、 The growing of grain is so highly dependent on technological factors that improvements in yield are unlikely, regardless of climatic conditions.
C、 Trends in rainfall patterns are more difficult to isolate than are trends in temperature.
D、 Long-range warming or cooling trends are more damaging to grain production if they are accompanied by changes in rainfall patterns than if they are not.
E、 (E) Long-range cooling trends are potentially more destructive to grain production than are long-range warming trends.

【正确答案】 D

【答案解析】[解析] 本题属于“无因就无果类型”的假设。本题的结论是“作物产量没有变化”，结论成立的前提是“在天气长期变暖或变冷的过程中，降雨形势没有发生变化”。很显然，如果前提条件不能满足，那么结论就很难成立。也就是说，如果在天气长期变暖或变冷的过程中伴随着降雨形势的变化，那么作物产量就会变化。由此分析可知本题结论显然是假定长期的变暖或变冷天气过程中伴随降雨形势的变化将比不伴随降雨形势的变化对农作物的产量影响大，即A→B。由此分析可知(D)为正确答案；(A)、(B)、(C)和(E)都是无关选项。