Which of the Following Illustrates the Process of Random Assignment

Which of the following illustrates the process of random assignment in an experimental study?

A) Participants are assigned to a group depending on whether or not they smoke.
B) Participants roll a die, and the number is used to assign them to one of six groups.
C) Participants are assigned to the "male" or "female" group depending on their gender.
D) Participants are asked which of two groups they prefer.