Answer:
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.