It makes sense that the research methodology would spit the groups, and you are correct, there has to be 2 groups of equal size. I did not even think about it. I have added this clarification to answer choice C.
C. Most cola drinkers prefer beverages without vinegar, even when they do not know vinegar is present.
Selected this because the wording and the given percentage seemed to suggest that we're considering the two groups of tasters a one big group and then by saying
The first group: almost two to one preference of vinegar over classic = approx. 66% of taster prefer vinegar. So approx. 33% prefer classic
The second group: 98% prefer classic
So now we have 33% classic + 98% classic vs 66% of vinegar + 2% of vinegar
Combined with the fact that most scientifically sound research should divide their subject into two groups of equal number of people to get a valid result the
It seems logical to conclude that (considering the entire research as a whole) "most cola drinkers prefer classic over vinegar, even when they do not know vinegar is present"Would it be more clear if we put in an addition clarification for this answer choice?