In double-blind studies neither the test subject or the researcher knows who was given the drug and who was given the control. why are these studies effective for testing a drug that may elevate mood and relieve feelings of depression?

a)since there are two symptoms that are affected, a double-blind study is required.
b)double-blind studies are ways to ensure that only the researcher can figure out who is getting the effective drug.
c)double-blind studies are the most economical way to gather results from testing on humans.
d)the patients and researchers are not given this information so