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
[{'content': 'Immunity may be natural or acquired. Which of the following best describes acquired immunity? \nSelect and explain. \nA. Increase in C-reactive protein (CRP), B. Presence of natural killer (NK) cells, C. Complement cascade, D. Maternal transfer of antibody', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Natural immunity is nonspecific. The description of natural immune functions described are not specific for a certain antigen. For example, certain proteins such as C-reactive protein (CRP) are acute-phase reactants. While elevated CRP is seen in infection, it is not disease-specific. Maternal transfer of antibody, however, is passive but still confers specific immunity. It is termed acquired immunity.', 'role': 'assistant'}]