What Is the Purpose of Randomization,or Random Assignment of Subjects,in

What is the purpose of randomization,or random assignment of subjects,in a study?

A) To ensure that all groups within a study are representative of the larger population.
B) To increase the chances that the study groups will be different from each other with regard to extraneous variables
C) To ensure that current events do not influence the outcomes of the study
D) To eliminate the need for establishing specific study criteria and subject eligibility