请教一个机经的答案

The quality of unrefined olive oil is not actually defined in terms of acidity, yet extensive tests have shown that the less free oleic acid an unrefined olive oil contains per liter, the higher its quality. The proportion of free oleic acid that an olive oil contains is an accurate measure of the oil’s acidity.

If the statements above are all true, which of the following conclusions is best supported by them?

A.When an olive oil is refined, the concentration of oleic acid in the oil is reduced.
B.The quality of an unrefined olive oil can be determined only by accurately measuring its acidity.
C.If an unrefined olive oil is intermediate in acidity between two other unrefined olive oils, it will also be intermediate between them in quality.
D.Free oleic acid is the only acid that unrefined olive oil contains.
E.People who judge the quality of unrefined olive oils actually judge those oils by their acidity, which the judges can taste.

我选A,请NN指点

选C

题目说free oleic acid 和quality成正比,而free oleic acid 又和 acidity成正比.也就是说 acidity和 quality成正比.

正好推出C.

A正好和题目相反