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

Explanation:

The double-blind test refers to the test performed in the medical research in which the information about the variable which has to be tested is not provided to both the participants and the researchers.

The experiment is usually performed to test the effect of drugs on the participants in which the placebos are involved. The double-blind experiment is performed to reduce the biases or error during the experiment.

Thus, in the given question the placebo involving experiment involves the double-blind experiment in which the placebos and drugs are provided to whom is not known.

Thus, Option-A is the correct answer.

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