Final answer:
Experts recommend that in vivo experiences in exposure therapy should not begin until the client has been desensitized to about 90% of the hierarchy items. Beginning in vivo experiences too soon may overwhelm the client and hinder therapeutic progress.
Step-by-step explanation:
In the context of therapeutic interventions, particularly those involving exposure therapy for anxiety disorders, experts generally recommend that in vivo experiences (real-life exposure) should not begin until the client has been desensitized to approximately 90% of the hierarchy items. A hierarchy in this sense refers to a graded series of anxiety-provoking situations that the patient will be gradually exposed to, starting with the least anxiety-provoking scenarios. Desensitization involves the client undergoing repeated exposures to these situations, either imagined or through 'in vitro' methods, and learning to manage their anxiety, until they can confront these situations without significant distress. Option 'c', which indicates 90%, is hence the correct response to the question. It is considered important to reach a high level of desensitization before progressing to in vivo experiences since premature exposure to real-life situations may be too overwhelming and counterproductive to the client’s progress.