When the pathogen enters the human body, it will stimulate lymphocytes to produce a special protein called antibody to resist the pathogen. The general measures to prevent infectious diseases can be divided into: controlling the source of infection, cutting off the route of transmission and protecting susceptible people. Source of infection: a person or animal that can spread pathogens. Transmission route: The route through which pathogens leave the source of infection and reach healthy people is called transmission, such as air transmission, food transmission and biological media transmission. Susceptible population: lack of immunity to some infectious diseases.
So choose: B.