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
[{'content': 'All of the following are features of Cross-Over studies except - \nSelect and explain. \nA. All patients receive the new therapy, B. Not suitable if drug on interest cures the disease, C. Not suitable if drug is effective only during a certain stage of disease, D. Not suitable if disease does not changes radically during the study', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]