TOEFL Listening: TPO-TOEFL阅读TPO - O6IC13FX2R0440L1N$

Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. A. Heat flows through solid rock very slowly, so it takes a very long time for geological processes to produce a reservoir of geothermal energy. B. Geothermal energy is not renewable because heat flows very slowly through solid rock into or out of a heat reservoir. C. The heat quickly removed from a heat reservoir is replaced so slowly by geological processes that geothermal energy is not practically speaking, renewable. D. In most cases, heat travels into a heat reservoir so slowly that it is a much quicker process to remove the heat from a reservoir than to replace it.