Bob Conducts a Three-Way Totally Between-Groups Study

Bob conducts a three-way totally between-groups study. Which of the following explanations of his study is correct?

A) There are two independent variables, each with three levels, and random assignment was used for all independent variables.
B) There are three independent variables, and random assignment was used for all independent variables.
C) There are three independent variables, with two of them using random assignment and one of them using correlated assignment.
D) There are two independent variables, each with three levels, with two of them using random assignment and one of them using correlated assignment.