问一道经济的题目,关于供需变化的!乙醇是一种无色、易燃的液体.当它与汽油混合就产生了一种可以代替汽油的新汽车燃料（简称“乙醇燃料”）.乙醇燃料的产量取决于乙醇的价格和汽油的

Question

问一道经济的题目,关于供需变化的!
乙醇是一种无色、易燃的液体.当它与汽油混合就产生了一种可以代替汽油的新汽车燃料（简称“乙醇燃料”）.乙醇燃料的产量取决于乙醇的价格和汽油的价格.因为乙醇燃料是汽油的替代品,汽油价格的增长推动了乙醇燃料的需求曲线右移（乙醇燃料需求量增加）.乙醇原料的供给量取决于乙醇的价格和玉米的价格（因为从玉米中提炼乙醇）.玉米价格的增长推动乙醇的供给曲线左移（乙醇供给量下降）.2008年上半年,美国市场上汽油的价格相比2007年大幅度增长,玉米的价格也增长.如何比较2008年上半年和2007年乙醇燃料的平衡价格（equilibrium price）的变化?
A.汽油价格的增长推动乙醇的需求曲线右移,此时增长的玉米价格推动乙醇的供给曲线左移.两种变化都使乙醇的价格下降.
B.汽油价格的增长推动乙醇的需求曲线右移,此时增长的玉米价格推动乙醇的供给曲线左移.两种变化使乙醇的价格持平.
C.汽油价格的增长推动乙醇的需求曲线右移,此时增长的玉米价格推动乙醇的供给曲线左移.两种变化使乙醇的价格上涨.
D.以上三种说法均有可能.因为汽油价格变化和玉米价格变化对对乙醇价格的影响比较模糊、无法确切计算.
上面是我的英文翻译版本~下面是英文原版：
Ethanol (i.e.,ethyl alcohol) is a colorless,flammable liquid
that,when blended with gasoline,creates a motor fuel that can serve as an
alternative to gasoline.The quantity of ethanol motor fuel that is demanded
depends on the price of ethanol and the price of gasoline.Because ethanol fuel
is a substitute for gasoline,an increase in the price of gasoline shifts the
demand curve for ethanol rightward.The quantity of ethanol supplied depends on
the price of ethanol and the price of corn (since the primary input used to
produce ethanol in the U.S.is corn).An increase in the price of corn shifts
the supply curve of ethanol leftward.In the first half of 2008,the price of
gasoline in the U.S.increased significantly as compared to 2007,and the price
of corn increased as well.How would the equilibrium price of ethanol motor fuel
in the first half of 2008 compare to the price in 2007?All of the above answers are possible because the combined impact
of the change in the price of gasoline and the price of corn on the price of
ethanol are ambiguous.The increase in the price of gasoline shifted the demand curve for
ethanol rightward,while the increase in the price of corn shifted the supply
curve for ethanol leftward.Both changes had the impact of decreasing the price
of ethanol.The increase in the price of gasoline shifted the demand curve for
ethanol rightward,while the increase in the price of corn shifted the supply
curve for ethanol leftward.Both changes caused the price of ethanol to remain
unchanged.The increase in the price of gasoline shifted the demand curve for
ethanol rightward,while the increase in the price of corn shifted the supply
curve for ethanol leftward.Both changes had the impact of increasing the price of ethanol.

Answer 1

选C 石油价格上涨,乙醇作为替代品需求量增加,需求增加价格就要上涨；玉米价格上涨,导致乙醇的供应量减少,供应量减少价格也要上涨.总之一句话,乙醇供不应求,价格当然上涨