Since the autumn and winter of 212, CCTV and other media have reported that with the frequent occurrence of "smog" weather, PM2.5 has gradually entered the public eye and atmosphere.

(1) Lung is suitable for human respiratory system. According to the title "Particulate matter with a diameter less than or equal to 2.5 microns in the atmosphere is called PM2.5, which is a fine particulate matter that can directly enter the lung. PM2.5 is the main cause of" smog ",which is rich in toxic and harmful substances, stays in the atmosphere for a long time and has a long transportation distance." It can be known that PM2.5 mainly harms human respiratory system. It passes through the nasal cavity, pharynx, larynx, trachea and bronchus, but PM2.5 particles are tiny, so it is not easy to be blocked by organs such as nose, and can directly enter the bronchus and alveoli, affecting the gas exchange in the lungs, causing asthma and other diseases. After entering the lungs, it can be quickly absorbed by capillaries outside the alveoli and distributed throughout the body through blood circulation. < P > (2) PM2.5 is the main cause of "smog" and is rich in toxicity. It has the characteristics of long staying time in the atmosphere and long transportation distance, so the more the content of PM2.5, the worse the air quality. On the contrary, the better the air quality, the correct C. < P > (3) Haze weather does great harm to human health, and the main reason for the formation of haze is PM2.5, so the main measure to avoid the harm of this weather to human body is to reduce the inhalation of PM2.5. ② It is best to wear a mask, walk and exercise when going out, and stay away from the driveway; (3) When the fog is heavy, try to close the windows and doors indoors. (Other reasonable answers are also possible)

(4) Straw burning pollutes the atmospheric environment, increasing the particulate matter and reducing the visibility; The second is to destroy the greening. In case the burning straw is out of control, it is easy to ignite the nearby forest and grass and cause a fire. Third, it causes a huge waste of resources. Fourth, it destroys the soil structure and causes the quality of farmland to decline. Fifth, the billowing smoke and patches of scorched earth formed by burning straw are the greatest damage to the environmental image of a city. (Just answer one correctly)

Straw is a good raw material and energy, which can not only pollute the environment, but also bring benefits to human beings, such as making paper, making biogas in biogas digesters, making feed after crushing, etc. (If the meaning is right, there must be at least two)

So the answer is Blood circulation;

（2）C；

(3) Wear a mask when going out, and it is best to stay away from the driveway when walking and exercising.

(4) firstly, the atmospheric environment is polluted, which increases the particulate matter and reduces the visibility; The second is to destroy the greening. In case the burning straw is out of control, it is easy to ignite the nearby forest and grass and cause a fire. The third is to cause huge waste of resources; Straw is a good raw material and energy. If used properly, it will not pollute the environment, but also bring benefits to human beings, such as paper making, biogas production in biogas digesters, and feed after crushing.