Since the autumn and winter of 2013, with the frequent occurrence of "haze" weather (pictured), PM2.5 has gradually entered the public eye. In the atmosphere, the diameter is less than or equal to 2.

Since the autumn and winter of 2013, with the frequent occurrence of "haze" weather (pictured), PM2.5 has gradually entered the public eye. In the atmosphere, the diameter is less than or equal to 2.5 micron

(1) The lungs are suitable for the human respiratory system. According to the question "Particles in the atmosphere with a diameter less than or equal to 2.5 microns are called PM2.5, which are small particles that can go straight into the lungs. PM2 .5 is the main reason for the formation of "haze". It is rich in toxic and harmful substances, and it stays in the atmosphere for a long time and is transported over a long distance. "It can be seen that PM2.5 mainly harms the human respiratory system. When air enters the lungs, it must pass through the nasal cavity, pharynx, larynx, trachea and bronchi. However, PM2.5 particles are so small that they are not easily blocked by the nose and other organs. They can directly enter the bronchi and alveoli, affecting the gas exchange in the lungs and causing diseases such as asthma. ． After entering the lungs, it can be quickly absorbed by the capillaries outside the alveoli and distributed throughout the body through blood circulation.

(3) Since PM2.5 is the main cause of the formation of "haze" and is rich in toxic and harmful substances, it has the ability to stay in the atmosphere for a long time and be transported over long distances

and other characteristics, so the higher the PM2.5 content, the worse the air quality is, and conversely, the better the air quality is.

(3) "Haze" weather causes great harm to human health. The main cause of "haze" is PM2.5. Therefore, the main measure to avoid the harm of this weather to human body is to reduce For inhalation of PM2.5, methods such as wearing a mask can be used. (Other reasonable answers are also acceptable)

So the answer is: (1) Breathing; bronchus; blood circulation;

(2) C;

(3) Plant trees and grass to increase the green area, promote green travel (cycling, taking the bus, not driving or driving less), reduce pollutant emissions, etc.; (points will be given as long as it is scientific and reasonable)