单项选择题

Taste is such a subjective matter that we don’t usually conduct preference tests for food. The most you can say about anyone’s is that it’s one person’s opinion. But because the two big cola companies -- Coca Cola and Pepsi Cola --are marketed so aggressively, we’ve wondered how big a role taste preference actually plays in brand loyalty. We set up a taste test that challenged people who identified themselves as either CocaCola or Pepsi fans: Find your brand in a blind tasting.
We invited staff volunteers who had a strong liking for either CocaCola Classic or Pepsi, Diet Coke, or Diet Pepsi. These were people who thought they’d have no trouble telling their brand from the other brand.
We eventually located 19 regular cola drinkers and 27 diet cola drinkers. Then we fed them four unidentified samples of cola one at a time, regular colas for the one group, diet versions for the other. We asked them to tell us whether each sample was Coke or Pepsi; then we analyzed the records statistically to compare the participants’ choices with what mere guesswork could have accomplished.
Getting all four samples right was a tough test, but not too though, for people who believed they could recognize their brand. In the end, only 7 out of 19 regular cola drinkers correctly identified their brand of choice in all four trials. The diet cola drinkers did a little worse -- only 7 out of 27 identified all four samples correctly.
While both groups did better than chance would predict; nearly half the participants in each group made the wrong choice two or more times. Two people got all four samples wrong. Overall, half the participants did about as well on the last round of tasting as on the first, so fatigue, or taste burnout, was not a factor. Our preference test results suggest that only a few Pepsi participants and Coke fans may really be able to tell their favorite brand by taste and price.
The author’s purpose in writing this passage is to ______.