The following are multiple choice questions (with answers) about medical knowledge.   **Question:** NK cells are effective against viral infected cells only if the cell with infection:   (A) Express MHC class I proteins   (B) Unable to express MHC class I proteins   (C) Express MHC class II proteins   (D) Unable to express MHC class II proteins
['(B) Unable to express MHC class I proteins <> answer', 'The following are multiple choice questions (with answers) about medical knowledge. <> instruction', '(A) Express MHC class I proteins \n (B) Unable to express MHC class I proteins \n (C) Express MHC class II proteins \n (D) Unable to express MHC class II proteins <> possible answers', '  NK cells are effective against viral infected cells only if the cell with infection: <> context@']