A.
Add 9 + 6.
B.
Add 6 + 6.
C.
Subtract 9 – 6.
D.
Subtract 6 – 6.
Results
Discussion
Bias
Answer:
The answer is D, bias. If bias were a factor in an observational study(which it is not), then the study would be inaccurate due to someone's personal views affecting the results. Therefore bias is not a factor in the process of evaluating an observational study.
I don't know who verified the answer of the person why thought the answer was A, but they were incorrect.