What Is a Reason That Alternating Treatments Designs May Have

What is a reason that alternating treatments designs may have good internal validity?

A) The patterns of response vary with the alternating treatment conditions, so there is minimal overlap among data in the conditions.
B) If one treatment is consistently associated with an improved level of responding, then the design demonstrates good experimental control.
C) It does not provide replication of the relative effects of the different treatments.
D) The patterns of response vary with the alternating treatment conditions, so there is minimal overlap among data in the conditions and if one treatment is consistently associated with an improved level of responding, then the design demonstrates good experimental control.