Which of the Following Is a Weakness of the Factorial

Which of the following is a weakness of the factorial design?

A) The study results become increasingly complex with the addition of more variables to the design.
B) The interaction of the independent variables with each other cannot be tested by this design.
C) Unexplained variance in the dependent variable is increased with the addition of related independent variables.
D) A maximum of five independent variables and their effects can be studied using this design.