Which Design Is Better, an A-B-A Design or an A-B-A-B

Multiple Choice

Which design is better, an A-B-A design or an A-B-A-B design?

A) A-B-A; it is more parsimonious
B) A-B-A; it has the ethical advantage of leaving subjects exactly where they started
C) A-B-A-B; it compares two different treatments
D) A-B-A-B; the treatment is evaluated twice