A medical study was investigating if getting a flu shot actually reduced the risk of developing the flu. From a group of adult volunteers, researchers randomly assigned half to receive an injection that contained the drug believed to reduce the risk of getting the flu and the other half to receive an injection containing no active ingredient (i. e. sugar water). Because the control group received a placebo, what type of study was performed?A. Blinded. B. Observational. C. Blocked. C. Confounded. D. None of the above.