The quality of unrefined olive oil is not actually defined

I wouldn't quite put it that way. B is contradicted by the passage -- it must be false. The first sentence in the passage tells us that the quality of olive oil is not defined in terms of acidity. So it must be assessed in some other way. So clearly there must be other ways, besides by measuring acidity, to judge the quality of olive oil.



Yes, using the 'same reasoning' for C won't work, because the reasoning wasn't correct. The question doesn't have anything to do with 'other aspects' that contribute to the quality of olive oil. It's only talking about how the quality of oil is measured. You might think of a different example: say in an elementary school, they don't use a ruler to compare the heights of the children (maybe they do it just by looking at the kids, or by standing them next to each other). But it turns out when you do use a ruler, the children the school judged to be tallest are actually tallest, and those judged to be shortest are actually shortest. The point is, we can measure height in different ways that lead to the same conclusions. The point is not that there are several factors that contribute to height that the ruler measurement ignores.