Why is it important in an experiment to test the effectiveness of a drug? O A. A placebo makes the sample less representative of the population but the data can still be used to make inferences about the population. O B. A placebo is important so that results from subjects given a treatment can be compared with the results from subjects given a placebo O C. A placebo makes the sample more representative of the population. O D. A placebo exaggerates any psychological differences between the control group and the treatment group