Seniors Who Identify Themselves as "Undecided" About Their Career Goals

Seniors who identify themselves as "undecided" about their career goals are more likely to add a second major than are seniors who report being "very clear" about their career goals. Which of the following is NOT a variable in this hypothesis?

A) class standing
B) degree of clarity about career goals
C) likelihood of adding a second major
D) They are all variables in the hypothesis.