Re: [CR. ] pp08 cr2-82

看板GMAT (GMAT入學考試)作者aolid (庫庫掃)時間15年前 (2011/05/31 01:42)推噓1(1推 0噓 0→)

留言1則, 1人參與討論串4/5 (看更多)

※ 引述《cindy0416 (ptt)》之銘言： : Technological improvements and reduced equipment costs have made converting : solar energy directly into electricity far more cost-efficient in the last : decade. However, the threshold of economic viability for solar power (that : is, the price per barrel to which oil would have to rise in order for new : solar power plants to be more economical than new oil-fired power plants) is : unchanged at thirty-five dollars. : Which of the following, if true, does most to help explain why the increased : cost-efficiency of solar power has not decreased its threshold of economic : viability? : A. The cost of oil has fallen dramatically. : C. Technological changes have increased the efficiency of oil-fired power : plants. : 答案是C，請問A為何不對呢？ : A和C在我看來都是差不多的。像C，就算效率提高，但油價仍然高漲的話，火力 : 發電還是很貴，太陽能電仍然有其效益。而A，則是油價提高，但不知道效率如 : 何。所以A和C似乎都不完整。 : 還是是我誤解了 "threshold of economic viability"的意思？這題我一開始也做錯了後來想了一想才開竅關鍵在threshold的定義 threshold是每桶油要漲到多少錢火力發電才會跟太陽能發電一樣貴這是個效率單位跟現在的油價無關假設過去要發100度電火力發電需要1桶油太陽能需要35塊所以過去的threshold是35塊後來太陽能發電進步了發200度電只需要35塊那為什麼threshold沒變呢? A 因為油變便宜了 C 因為火力發電進步了先看A 就算油價下跌如果效率不提升 threshold還是會改變 (火力發電要發200度電需要2桶油 threshold會變成17.5) 就算今天一桶油跌到剩1塊一桶油還是要$17.5 才會讓兩邊的成本一樣再看C 因為火力發電也進步了一桶油可以發200度電新的threshold還是35塊只有C才能讓題目要的條件成立 -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 118.169.172.205 ※ 編輯: aolid 來自: 118.169.172.205 (05/31 01:45)