Subjects in an experiment for an herbal cold medicine either receive a tea made from the herb, or a placebo tea. Their doctor also doesn't know which tea was distributed to which subject. This experiment is .

A double blind experiment

Explanation:

A double-blind experiment refers to an experiment in which the information about the treatment of the studied variable is provided to neither the researcher nor the participant. In this type of experiment, both the participant and the experimenter are unaware that which participant has got the experimental treatment.

This test is used by the drug researcher in which the placebo treatment along with experimental treatment is provided.  This experiment is performed to ensure that the results are unbiased and the chances of errors and prediction get reduced.

Thus, A double-blind experiment is correct.

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