Which of these is not an acceptable method of ensuring that

Which of these is not an acceptable method of ensuring that experimental and control groups are similar? Select one: a. Match pairs of subjects on relevant variables, and assign one from each pair to each group b. Encourage members of the control group and the experimental group to communicate freely with one another throughout the experiment c. Create groups that are equivalent in terms of their averages on some relevant variables d. Assign subjects randomly to the experimental and control groups

Solution

d. Assign subjects randomly to the experimental and control groups