You Are a Doctor Who Examines a Swollen and Warm

You are a doctor who examines a swollen and warm puncture wound on the hand of a patient. Because the wound was made by a rusty nail, you are concerned about infection by Clostridium tetani bacteria, which cause tetanus. You are relieved to see that the patient received a tetanus vaccine at her last checkup a year ago. The vaccine:

A) exposed the patient to C. tetani so that she contracted a mild version of tetanus.
B) exposed the patient to deactivated C. tetani, so that her B cells would produce antibodies to the bacteria with no risk of contracting the disease.
C) stimulated the production of mast cells by her bone marrow.
D) exposed the patient to other types of bacteria, so that her immune system would be prepared for infection by prokaryotes.