This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Which one of the following statements regarding pre-post clinical trial is most appropriate - 
Select and explain. 
A. They cannot be randomized, B. They are useful in studies involving mortality, C. They use the patient as his or her own control, D. They are usually easier to interpret than the comparable parallel clinical trial
C: They use the patient as his or her own control
Answer: C: They use the patient as his or her own control 
Explanation: None