B

　　The influenza virus(流感病毒) or the flu is spread from person to person in the air when an infected person coughs or sneezes.There are 3 types of the flu：

　　—Type A viruses can infect people，birds，pigs，horses，seals，whales，and other animals，such as avian flu or bird flu.

　　—Type B viruses infect people and result in smaller outbreaks(爆发)．People infected with type B viruses are often hospitalized with higher death rates.

　　—Type C viruses cause mild illness in humans without the onset of an epidemic (流行病)．

　　Most people are familiar with the symptoms of the flu，but they can be mistaken for a severe cold.The flu infection is far more serious and can cause severe health complications (并发症)．There are many viral infections that can cause flu­like symptoms.It is better to visit your doctor so other possibilities can be ruled out before your obtaining treatment.

　　The flu virus attacks the body's cells and changes into different forms，which is why people who have received the flu shot (流感疫苗接种) may still get ill with the flu.The influenza virus is transmitted_ through direct contact with infected persons such as by inhaling (吸入)droplets when they have coughed or sneezed.It can also be spread by handling objects such as doorknobs and telephone receivers that an infected person has been in contact with.

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