This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Haematology, Subject name: Anatomy
Adult patient presents with generalized lymphadenopathy and blood film shows 70percent immature looking lymphocytes. What should be the next best investigation? 
Select and explain. 
A. Genotyping/karyotyping, B. Immunophenotyping, C. Bone marrow, D. Peripheral smear study
B: Immunophenotyping
Answer: B: Immunophenotyping 
Explanation: Adult pateint presenting with generalized lymphadenopathy and blood film shows 70percent immature looking lymphocytes is highly suggestive of chronic lymphocytic leukemia. Immunophenotyping can be one of the best ways to differentiate between CLL and other B cell neoplasms.( ref Robbins 9/e p593)