With One Exception, All of the Following Present Challenges or Barriers

With one exception, all of the following present challenges or barriers to rigorously studying sensory integration (SI) and answering the question, "Does SI intervention work?" Which of the following is NOT a barrier?

A) Finding ways to detect central nervous system (CNS) change as a result of SI intervention
B) Funding; it is a relatively expensive and labor-intensive intervention
C) Identifying meaningful outcome measures when goals of therapy inherently vary across study participants
D) Ability to recruit subjects with SI problems because the condition is so rare