Which of the Following Statements About Independent and Dependent Variables

Which of the following statements about independent and dependent variables is true?

A) All research problem statements must contain a dependent variable and an independent variable.
B) There should only be one dependent variable associated with a single independent variable.
C) The relationship between the independent variable and the dependent variable for any study must be causal.
D) A given characteristic or situation may be a dependent variable in one study and an independent variable in another.