Assertion (A): Natural killer (NK) cells are part of the adaptive immune system. Reason (R): They recognize and kill virus-infected cells and some tumor cells without prior sensitization.
- ABoth A and R are true and R is the correct explanation of A
- BBoth A and R are true but R is NOT the correct explanation of A
- CA is true but R is false
- DA is false but R is true
✓ Correct answer: D
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