Final answer:
Assisting a patient with a prescribed exercise routine is a patient-related task for a physical therapy aide.
Step-by-step explanation:
The activity of a physical therapy aide that would be defined as a patient-related task is assisting a patient with a prescribed exercise routine (option C). This involves working directly with the patient to guide and support them during their exercises, ensuring they are performed correctly and safely. This type of activity is important for helping patients improve their physical functioning and reduce impairments under the supervision of a physical therapist.