gwd1-30

Q30:

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 ?

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

  
Answer:

I guess you should have confusion in C. However, C can be true only assuming a linearity between acidity of the oil and the proportion of the oleic acid in the oil. However, this linearity is not implied in the original text which states only to the extent of measurability, not how it will be measured. After all, other nonlinear relationship, such as a quadratic one, between the proportion of oleic acid and the acidity can suffice an accurate measurement.

B is true. If you can use property A to measure, accurately, property B, you can do the reverse-although it is posible that the reverse may not give you a single outcome, it nevertheless will be a measurement, and the outcomes will all be accurate.