Final answer:
Patients receiving therapy for a psychological problem improve more than 60% of people with similar problems who do not receive treatment.
Step-by-step explanation:
The question is asking about the average improvement of patients receiving therapy for a psychological problem compared to people with similar problems who do not receive treatment. The correct answer is c) 60%. This means that, on average, patients receiving therapy improve more than 60% of people with similar problems who do not receive treatment.