Answer:
It is not a reliable test because the people's answer may be biased by prior familiarity with the brands they are testing.
Explanation:
The results are most likely unreliable because if the people who are testing the two brands of lemonades (brand X and Y) know the two brands already from before the test, their responses may be biased according to what they believe a priori that is better. In other words, they could simply choose their favorite brand without objectively analyzing the taste.