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': 'The reaction between antibody and soluble antigen is demonstrated by - \nSelect and explain. \nA. Agglutination, B. Precipitation, C. Complement fixation test, D. Hemagglutination test', 'role': 'user'}, {'content': "Answer: B \nExplanation: When a soluble antigen companies with its antibody in the presence of electrolyte at a suitable temp & pH the antigen-antibody complex forms an insoluble precipitate. Ref: Ananthanarayan & Parker's textbook of microbiology 9th edition pg:105", 'role': 'assistant'}]