The disease asthma affects as many as one hundred fifty million people around the world. It is a serious lung disease that causes breathing problems. These problems, called asthma attacks, can kill people. Asthma can affect people of all age groups but often begins in childhood. It can be controlled but not cured. Sufferers must deal with the disease every day.

Experts say exercise is one of the things that can start an asthma attacks. Things that lead to asthma attacks are called triggers. Although doctors do not know the cause of asthma, they have identified(辨认)most of its triggers. For example, the common cold can cause an asthma attack in a person who has the disease. There are also several air pollutants(污染物)that can lead to an asthma attack. Pollen is one such pollutant. Pollen is a fine dust that comes from plants that produce seeds. However, almost any kind of dust can cause an asthma attack if enough of it is in the air. This includes common dust found in houses.
Air pollution from burning fuel also can cause an asthma attack. Tobacco smoke can do the same. Some kinds of animal fur are a trigger for asthma. And, even some insects(昆虫)in the home can lead to asthma attacks.
Several things happen in the lungs when an asthma sufferer has an attack. Cells in the air passages begin to produce too much of a thick, sticky material called mucous(痰). The mucous creates blocked areas in the air passages. The tissue(组织)that lines the air passages begins to expand at the same time. And, the muscles in the passages tighten.
All these changes cause the air passages to narrow. This reduces the amount of air that can flow in and out of the lungs. The sufferer can not get a good, deep, breath of air. The narrowed airways also cause coughing and a tight feeling in the chest.
Which of the following statements about the disease asthma is NOT right?

A．It causes breathing problems, which can have sufferers killed.

B．It can not be cured but can be controlled.

C．People of all age groups can get affected, especially the old.

D．Doctors know little about its cause.

How many triggers of the disease asthma are mentioned in the text?

A．5.

B．6.

C．7.

D．8.

What an asthma sufferer should NOT do is________.

A．do as much exercise as possible

B．try to avoid catching cold

C．keep away from pollen

D．deal with the disease every day

What is the main idea of the last two paragraphs?

A．The mucous is the main cause of the disease asthma.

B．What happens in the lung cause an asthma sufferer to have trouble in breathing.

C．The sufferer can not get a good, deep, breath of air.

D．The disease asthma, caused by mucous, can be prevented.