Why Is Randomization Used to Assign Research Participants to Groups

Why is randomization used to assign research participants to groups?

A) to prevent assembling groups that differ in a way that may influence the research outcome
B) to make sure that all participants in the study are the same on the dependent variable when the study is concluded
C) to make sure that all participants are the same on the independent variable before the study begins
D) to prevent any differences in the way the independent variable is manipulated for all research subjects