请教一道新东方新书的逻辑题

求教：新东方逻辑新书P60 No.164. 实在是看不懂这个长句，或者大家有不用看懂这句话就能选出答案的方法，也请赐教。万分感谢！

Hotco oil burners,designed to be used in asphalt plants, are so efficient that Hotco will sell one to the Clifton Asphalt plant for no payment other than the cost savings between the total amount the asphalt plant actually paid for oil using its former burner during the last two years and the total amount it will pay for oil using the Hotco burner during the next two years. On installation, the plant will make an estimated payment, which will be adjusted after two years to equal the actual cost savings.

which of the following , if it occurred, would constitute a disadvantage for Hotco of the plan described above?

A. another manufacturer's introduction to the market of a similarly efficient burner

B. the Clifton Asphalt plant's need for more than one new burner

C. very poor efficiency in the Clifton Asphalt plant's old burner

D. a decrease in the demand for asphalt

E. a steady increase in the price of oil beginning soon after the new burner is installed

burners are so efficient that Hotco will sell one to the Clifton Asphalt plant for no payment other than the cost savings between 。。。 and 。。。（即只付用H的炉和旧炉所节省的油钱）

答案为D，即如果该厂的产品产量减少（a decrease in the demand for asphalt ），则节省的油钱也少，而H只受节省的油钱，对其计划不利

SORRY, 又是一道SHELL GAME，看得快就掉进去，某个厂的产量变化和整个市场的需求没有必然关系。H收的节省的油钱是旧的炉减去H的炉，所以油价涨对其不利。还是E好。原来想倒了，以为E是支持。

e为什么不对呢？

Hotco收的是两者的差价，即 两年前用的钱-现在用的钱， 现在油价升了，被减数增大，它收的钱肯定会减少呀。且文中并没提根据价格调整。另外问中好像没提沥青产量和耗油量的关系。请指教

the cost savings between the total amount the asphalt plant actually paid for oil using its former burner during the last two years and the total amount it will pay for oil using the Hotco burner during the next two years

我明白了，谢谢大家的帮忙！