Answer: d. double-blind
Explanation:
A double blind study can be define as the study in which both the researcher and participant do not know which participant is receiving a particular treatment. This method is useful as it prevents the bias in the results of the experiment.
The given situation is the example of double-blind study. Here, the participants as well as the researcher do not know which group of subject are receiving bacteria in the yogurt and which group is not receiving.
Atrial fibrillations the problem of irregular heartbeats, due to which clots can form inside the veins, and may lead to stroke, and ultimately, heart failure. An anticoagulant is given to such patients, to decrease the chances of occurrence of a heart attack due to blood clot formation.
