This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Immunology, Subject name: Microbiology
In an inflammatory response, macrophages are usually derived from - 
Select and explain. 
A. Monocytes, B. Reticuloendothelial cells, C. Neutrophils, D. Lymphocytes
A: Monocytes
Answer: A: Monocytes 
Explanation: When a monocyte enters damaged tissue through the endothelium of a blood vessel, a process known as the leukocyte extravasation, it undergoes a series of changes to become a macrophage. Reff: Ananthanarayanan & Panikers textbook of microbiology 9th edition pg: 137