6. In paragraph 3, why does the author mention that in the 1990s The Geysers was in its third decade of production?

　　○ To provide the historical context of the geothermal production of electricity in the United States

　　○ To imply that The Geysers was the first geothermal site to be put into production in California

　　○ To help explain the signs of decline shown by The Geysers

　　○ To explain why 70 new geothermal sites were put into electricity production in the late 1990s

　　题型：修辞目的题

　　定位词： in the 1990s The Geysers was in its third decade of production

　　解题思路：这是例证目的题，答案在例子的后半句，“该设施当时在其生产的第三十年”是用来更好地说明其下降的迹象。所以c项正确。

　　重点句子翻译：

This facility was then in its third decade of production and was beginning to show signs of decline, perhaps because of over development.

该设施当时在其生产的第三十年，开始显示出下降的迹象,也许是因为过度开发。