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
Innate immunity active againts viral cells - 
Select and explain. 
A. NK cells, B. Cytotoxic T cells, C. B cell, D. Memory B cell
A: NK cells
Answer: A: NK cells 
Explanation: NK cells are considered as an innate immune defence against cells that have lost the expression of ClassI MHC like virus infected cells and malignant cells. Reff: Ananthanarayanan & Panikers textbook of microbiology 9th edition pg: 137