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: Pathology
The histiocytosis X is a spectrum of disorders, which include the following condition 
Select and explain. 
A. Eosinophilic granuloma, B. Hand Schuller - Christian disease, C. Letterer - Siwe disease, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None