A、One. B、Two. C、Three. D、Four. C本题属于事实细节题。本题的难点是要统计文中提到的泳池中的细菌引起的疾病有几种，需要仔细听辨。文中提到的有：diarrhea illness、ear infection called“swimm

Everybody loves the swimming pool. But how clean is the water in the average backyard or public pool? If you trust chlorine to take care of germs, you’re in for a surprise.
    Chlorine and other disinfectants do indeed help to clean the water, but some germs can survive in even the best-kept pool. For example, cryptosporidium may live in pool water for several days. Crypto causes a diarrhea illness and may rinse off the bodies of infected people or diapered children into the pool. If you swallow infected pool water, you may become sick.
    Other germs may live for a few minutes or a few hours in a chlorinated pool: Giardia, Shigella, and E. Coli may cause diarrhea illnesses. Pseudomonas Aeruginosa may cause an ear infection called swimmer’s ear and also a skin infection called "hot tub rash", that is usually associated with very warm pools and spas.