单选题 15. Although many brands of gasoline are sold on Haibei Island, gasoline companies there sell all of the refined gasoline from Haibei seaport's only storage tank, which is always refilled with the same quality of gasoline. Therefore, the brands of gasoline for sale on Haibei may be different in name and price, but they are identical in quality.
The conclusion drawn above depends on which of the following assumptions? ______

A、 Consumers are usually unaware of variations in the quality of the gasoline they buy unless those variations are announced by the gasoline companies.
B、 When tankers make gasoline delivery at Haibei's seaport, the storage tank at Haibei always receives the same quantity of gasoline as that in the preceding delivery.
C、 There is a wide variation in the price at which the different brands of gasoline on Haibei are sold.
D、 If any gasoline company on Haibei alters the quality of its gasoline before sale, the other gasoline companies also use methods before sale that result in the same change in the quality of their gasoline.
E、 The gasoline storage tank on Haibei's large enough to meet the needs of all of Haibei's different gasoline companies.

【正确答案】 D

【答案解析】 D：选项取反。如果有的公司品质变了，另外的公司不会发生同样的变化一各家石油品质不一样，削弱原文，正确。
A：本文讨论的是海北各家石油公司售卖的石油的变化，与消费者是否意识到这些变化无关，不选。
B：本文讨论的是石油的品质，与数量无关，不选。
C：本文讨论的是石油的品质，与价格无关，不选。
E：油罐大，这是石油的数量问题，与品质无关，不选。