Abdul has volunteered to participate in an experiment evaluating the effectiveness of aspirin. Neither he nor the experimenters know whether the pills he takes during the experiment contain aspirin or are merely placebos. The investigators are apparently making use of .

B). The double blind procedure.

Explanation:

'The double blind procedure' is demonstrated as the procedure or method of experiment in which both the experimenter as well as the subjects or participants of the experiment are 'blind to' or 'unaware' of the crucial/significant aspects like hypothesis of the experiment

As per the question, the 'double blind procedure' is being employed by the investigators as neither the subject of the experiment nor the experimenter know about the 'experiment containing aspirin or mere placebos' which would help in producing the objective and unbiased deductions. Thus, option B is the correct answer.

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