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: Pharmacology
Orphan drugs are: 
Select and explain. 
A. Drugs with high therapeutic failure, B. Drugs with high toxicity, C. Drugs having low therapeutic margin, D. Drugs for rare disease
D: Drugs for rare disease
Answer: D: Drugs for rare disease 
Explanation: None