Before experimental drugs can be brought to market, they must undergo many rigorous trials to ensure they deliver their medical benefits effectively and safely. One method commonly used in this process is to compare the effect of a drug with that of a placebo in double-blind tests. A) Neither the researchers nor the study participants know who is receiving the drug and who is receiving the placebo. In controlled experiments:B) one variable is manipulated while others are held constant. C) none of these

Option A, Neither the researchers nor the study participants know who is receiving the drug and who is receiving the placebo.

Explanation:

In a double blind test, both the researcher and research participants are unaware of the exercise in a medical test . During the research active medication is given to some of the research participants making sure that researcher is unaware of that while observing all the participants. However, at the end of the experiment ,both the researcher and research participants get to know who has received the treatment.

Hence, option A is correct

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