Final answer:
Legionnaires' disease is caused by the bacterium Legionella pneumophila, which is spread through aerosols from contaminated water sources.
Step-by-step explanation:
Legionnaires' disease is an atypical form of pneumonia caused by the bacterium Legionella pneumophila. This pathogen infects amoebae in moist environments and can spread to humans through aerosolized water from sources like air-conditioning cooling towers and humidifiers. The correct answer to which bacteria causes Legionnaires' disease is B) Legionella pneumophila.
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