This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chronic Lymphocytic Leukemia, Subject name: Pathology
Examination of a peripheral blood smear demonstrates leukemia composed of small mature lymphocytes without blast forms. Which of the following is the most likely age of this patient? 
Select and explain. 
A. 1 year, B. 20 years, C. 45 years, D. 65 years
D: 65 years
Answer: D: 65 years 
Explanation: The disease described is chronic lymphocytic leukemia (CLL), which is a disease of older adults. The 1 year-old (choice A) would be most likely to have acute lymphocytic leukemia (ALL). The 45 year-old (choice C) would be likely to have either AML or chronic myelogenous leukemia (CML).