Answer:D.double-blind, random selection, placebo-controlled.
Step-by-step explanation:
A double-blind study is a study in which both the participants and the experimenters are not aware of the kind of treatment that they would be or are receiving during the experiment , so they are both left in the blind.
It is done to eliminated bias results from the experiment especially bias result that may be brought up by the placebo effect.
Random selection means participants are selected from the whole population and then randomly assigned to either experimental or control group. This is observed when Dr Sullivan uses the hat to draw the names of the students to decide if they will be in the experimental group or control.
Placebo-controlled refers to a sugar pill given to other participants which has no medical effect or any other effect this is used to test a medical therapy , sugar pill still resembles the Z vitamin capsule so that participants won't know that it is placebo.