Why Is the Practical Application of the Four-Group-Six-Study Design Somewhat

Why is the practical application of the four-group-six-study design somewhat limited in marketing?

A) The design is expensive in terms of time.
B) Marketing samples are not always large enough to divide the samples of test units into four groups.
C) If the group samples are small, it is unlikely they will be equal even if assigned randomly.
D) The design is expensive.
E) All of the above.