Good question. I'm going to input some numbers so that you can see why the argument is flawed. This is actually a pretty common flaw on the test, so it is important that you understand quantity vs. percentage.
Let's say there are 100 sociology majors. Most of them are taking Intro to Social Psychology. We will call it 60%. That is 60 sociology majors in the class.
Let's say there are 200 psychology majors. Most of them are not taking Intro to Social Psychology. We will say only 40% are taking the class. That is 80 psychology majors in the class.
60 soc. majors and 80 psych. majors means that the conclusion is invalid. What was the flaw here? The author assumed that the two major groups were of the same size. You cannot compare percentages of two groups unless we know the size of each of those groups.
So which answer choice makes the same error? That would be D. Do we know the total number of vegetables at Valley Food Co-Op or at Jumbo Supermarket? No, so we have no way to compare them. The majority of organic vegetables at VFC could still be a smaller number than the minority of organic vegetables at Jumbo. The conclusion is not valid.
