Would It Be Possible for a Scientist to Bias a Scientific

Would it be possible for a scientist to bias a scientific study?

A) No,there are so many checks and balances outside of the scientist's control that it's impossible to show bias in a scientific study.
B) No,because all scientific experiments are designed to be fair.
C) Yes,if the scientist used a large number of test subjects.
D) Yes,if the scientist chose specific individuals to include in the study.
E) Yes,if it was a randomized double-blind study.