The correct answer is D. Through random selection
Explanation:
In a research study, it is common researchers have a control group and an experimental group. In this way, the experimental group is the one that receives a special treatment, for example, the experimental group is given a medicine to treat a disease. On the other hand, the control group is not given a treatment and it is used as a standard to measure the effect of the treatment.
Both the control and the experimental group are usually selected randomly, this guarantees in each group there is diversity and the study is not influenced. For example, if the researcher is studying the effect of a teaching method on the result of some test, it is important in both the control and the experimental groups there are students with different features such as academical performance, which can be guaranteed if there is a random selection.
