When germs，such as bacteria or viruses，invade the body，they attack and multiply. （1）BBThe immune system uses several tools to fight infection（感染）.Blood contains red blood cells，for carrying oxygen to tissues and organs，and white or immune cells，for fighting infection.These white cells consist primarily of macrophages（巨噬細(xì)胞），B cells and T cells.
Macrophages swallow up and digest germs，plus dead and dying cells.They leave behind parts of the invading germs called antigens（抗原）. （2）EEB cells are defensive white blood cells which produce antibodies.T cells are also defensive white blood cells.They attack cells in the body that have already been infected.
The first time the body comes across a germ，it can take several days to make and use all the germ fighting tools needed to get over the infection.After the infection，the immune system remembers what is learned about how to protect the body against that disease.
（3）AAThey help develop immunity by imitating an infection.This type of infection，however，almost never causes illness，but it does cause the immune system to produce T cells and antibodies.Sometimes，after getting a vaccine （疫苗），the imitation infection can cause minor symptoms.For instance，a fever. （4）FF
Once the imitation infection goes away，the body is left with a supply of defensive cells that will remember how to find that disease in the future. （5）GGTherefore，it is possible that a person infected with the disease just before or just after vaccination could develop symptoms and get a disease，because the vaccine has not had enough time to provide protection.
A.Vaccines basically work the same way.
B.This invasion，called an infection，is what causes illness.
C.Vaccines prevent diseases that can be dangerous，or even deadly
D.Scientists take many different approaches to developing vaccines.
E.The body identifies them as dangers and excites antibodies to attack them.
F.Such minor symptoms are normal and should be expected as the body builds immunity.
G.However，it typically takes a few weeks for the body to produce those defensive cells after vaccination.
【考點】人與自我．
【答案】B；E；A；F；G
【解答】
【點評】
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發(fā)布：2024/6/27 10:35:59組卷：4引用：1難度：0.5
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