请教两道逻辑题~~~理解不了~~~~help

1、Although many brands of gasoline are sold on Haibei island, gasoline companies there get all of the refined gasoline they sell 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 assumption?

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 an Hailed 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 compnay 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.
我选了B
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2、Although the ratio of physicians to total population is about the same in the United States and Canada, the United States has 33 percent more surgeons per capita. Clearly, this is the reason people in the United States undergo 40 percent more operations per capita than do Canadians.

The explanation given above rests on an assumption that

A) patients in the United States do not have a greater need for surgery than do patients in Canada.

B) the population of the United States is not larger than that of Canada.

C) United States patients sometimes travel to Canada for certain kinds of surgery.

D) general practitioners in the United States do not as a rule examine patient who is a candidate for surgery before sending the patient to a surgeon.

E) there are no unnecessary surgical operations performed in Canada.
我选了E

我做错了，不是太明白。。。
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答案：1 D
2 A