参考答案：A

解析：
Prompted by the oil crises of the 1970s, a wind-power industry flourished briefly in the United States. But then world oil prices dropped, and funding for research into renewable energy was cut. By the mid-1980s US interest in wind energy as large-scale source of energy had almost disappeared. The development of wind power at this time suffered not only from badly designed equipment, but also from poor long-term planning, economic projections that were too optimistic and the difficulty of finding suitable locations for the wind turbines.

[分析]： 因果关系的找寻和判断。
题干要求弄清楚20世纪80年代美国风能产业走弱的原因。根据原文Prompted by the oil crises of the 1970s，a wind-power industry flourished briefly in the United States．But then world oil prices dropped，and funding for research into renewable energy was cut. 20世纪70年代的石油危机使风能产业兴盛，而后来油价的下降使得用于可再生能源的研究基金被削减。由此可推测，风能的研究因此受到影响，势头减弱。因此A的说法“因为20世纪70年代的石油危机”与原文不符。
[解题关键] 掌握表示转折关系的信号词，如本题中根据but判断其前后的句子含义，可帮助推测出正确的因果关系。