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
NK cells are - 
Select and explain. 
A. Activated macrophages, B. Antibody-activated T cells, C. Null cells activated by complement, D. Independent of antibody
D: Independent of antibody
Answer: D: Independent of antibody 
Explanation: NK cells are unique, however, as they have the ability to recognize stressed cells in the absence of antibodies and MHC, allowing for a much faster immune reaction. They were named "natural killers" because of the initial notion that they do not require activation to kill cells that are missing "self" markers of MHC class 1. Reff: Ananthanarayanan & Panikers textbook of microbiology 9th edition pg:137