Questions 11 to 15 are based on the following passage.
Scratchy throats, stuffy noses and body aches all spell misery, but being able to tell if the cause is a cold or flu (流感) may make a difference in how long the misery lasts.
The American Lung Association (ALA) has issued new guidelines on combating colds and the flu, and one of the keys is being able to quickly tell the two apart. That’s because the prescription drugs available for the flu need to be taken soon after the illness sets in. As for colds, the sooner a person starts taking over-the-counter remedy, the sooner relief will come.
The common cold and the flu are both caused by viruses. More than 200 viruses can cause cold symptoms, while the flu is caused by three viruses―flu A, B and C. There is no cure for either illness, but the flu can be prevented by the flu vaccine (疫苗), which is, for most people, the best way to fight the flu, according to the ALA.
But if the flu does strike, quick action can help. Although the flu and common cold have many similarities, there are some obvious signs to look for.
Cold symptoms such as stuffy nose, runny nose and scratchy throat typically develop gradually, and adults and teens often do not get a fever. On the other hand, fever is one of the characteristic features of the flu for all ages. And in general, flu symptoms including fever and chills, sore throat and body aches come on suddenly and are more severe than cold symptoms.
The ALA notes that it may be particularly difficult to tell when infants and preschool age children have the flu. It advises parents to call the doctor if their small children have flu-like symptoms.
Both cold and flu symptoms can be eased with over-the-counter medications as well. However, children and teens with a cold or flu should not take aspirin for pain relief because of the risk of Reye syndrome (综合症)，a rare but serious condition of the liver and central nervous system.
There is, of course, no vaccine for the common cold. But frequent hand washing and avoiding close contact with people who have colds can reduce the likelihood of catching one.
 

We learn from the passage that （）