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
Periodic acid schiff stain shows block positivity with following cell line: 
Select and explain. 
A. Myeloblasts, B. Lymphoblasts, C. Monoblasts, D. Megakaryoblasts
B: Lymphoblasts
Answer: B: Lymphoblasts 
Explanation: Leukemic lymphoblasts react with periodic acid schiff (PAS) stain gives reddish-purple clumps, sometimes more rectangular in character and referred to as "block" positivity (as opposed to the fine granular staining that can be seen in some myeloblasts and other cells). Ref: Lichtman M.A., Shafer J.A., Felgar R.E., Wang N. (2007). G. Lymphocytic Leukemias. In M.A. Lichtman, J.A. Shafer, R.E. Felgar, N. Wang (Eds), Lichtman's Atlas of Hematology.