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: Medicine
Drug of choice in chronic lymphatic leukemia is: 
Select and explain. 
A. Busulphan, B. Vincristine, C. Chlorambuccal, D. Mercaptopurine
C: Chlorambuccal
Answer: C: Chlorambuccal 
Explanation: None