Sometimes a behavior (like language) will not return to baseline levels after your treatment has been successful. For example, a previously nonverbal child is unlikely to become nonverbal again after you successfully teach him to talk. In this example, design would be a bad choice, and design would be best.

Hello the options to your question is missing below are the missing options

a ABA; ABAB design

b changing criterion design; Interaction design

c ABA; multiple baseline design across participants

d interaction design, alternating treatments design

answer :  ABA; ABAB design   ---  ( A )

Explanation:

In this example ABA design would be a bad choice, and ABAB design would be best

ABA also known as applied behavioral analysis used to improve social communication and it is a bad choice because it cannot be used to test/ return a behavior,  while ABAB ( reversal design ) is used to test if an intervention was effective hence it is the best choice to ensure that the intervention is not returned back to baseline.