In order to determine the effects of a new pill that is supposed to reduce hair loss, a researcher conducts a study. Five hundred volunteer subjects (300 men and 200 women) all of which suffer some degree of hair loss are selected to participate in the study. The researcher gives the women the real pill and the men a sugar pill, but only the researcher knows this.The results of this study are likely to be invalid mostly because
A. the gender of the patient could be a confounding variable in this study.
B. the subjects were volunteers.
C. the subjects did not know if they were getting the real treatment.
D. the treatment group and control group were not the same size.
E. none of these
Answer: A
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A. 
B. 
C. 
D. 
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