16．The immune system is the body's defender．It identifies，tracks own，and destroys troublemakers before they can hurt the body．Those troublemakers may be，for example，bacteria from a cut or splinter，a measles（麻疹） germ，a cold bug，or even a cancer cell．?
These invaders try to take over our tissues and feed off our bodies'nutrients．If they succeed，we become sick or，sometimes，even die．It's the job of our immune systems to destroy these invaders before they destroy us．?
Say you picked up a flu virus last week．Perhaps it entered your body through a cut，from a drinking glass，or from the air you breathe．Of course，you didn't feel it，but the virus made its way into your bloodstream．As soon as it entered your body，it began to reproduce．Viruses have only one goal：to take over your cells．Once inside your body，viruses try to enter cells and disrupt their normal wor k．If left alone，these viruses would hurt so many cells that you would weaken，or worse，get a serious illness．?
But this flu virus should not be so complacent as it seems to be．As it repoduces in your bloodstream，the virus is met by a certain kind of white blood cell，the lymphocytes．The lymphocytes are the foot soldiers that keep you alive．?
The number of lymphocytes in your body is hard to imagine．Thousands of them could fit in the period at the end of this sentence．Your body holds about a trillion-that's 1，000，000，000，000 of them，or about 3，000 in every drop of blood．Since you began reading this sentence，over 800，000 of them have been created and destroyed．?
Some of these lymphocytes pass through a small walnut?sized organ called the thymus．The thymus is the base of the neck．Here，special hormones（荷尔蒙）turn lymphocytes into fighting cells，called T ells．?
T cells have one terrific talent：They can tell the difference between friend and foe；what should be in our bodies and what shouldn't．They do not affect the body's healthy cells．Yet they attack everything that is foreign to our bodies，such as germs，transplants，and even our own cells which have become abnormal，as in the case of cancer．
28．What is the function of our immune system？C
A．To take over our tissues an feed off our bodies'nutrients．
B．To prevent bacteria or germs from entering the body．
C．To destroy the troublemakers in order that they might not hurt the body．
D．To fight against T cells．
29．Which of the following can NOT be detected by T cells？A
A．Thymus．
B．Transplants．
C．Cancer cells．
D．Healthy cells．
30．Which of the following questions best summaries the main idea of the whole passage？B
A．How does the immune system attack the flu virus？
B．How does the immune system function in our body？
C．How do the lymphocytes work in our body？
D．What is the so called immune system？
分析 本文属于说明文阅读，作者通过这篇文章主要向我们描述了免疫系统是人体的卫士，可以识别，跟踪自己，破坏可以伤身体的捣乱者
解答 28．C．细节理解题．根据第一段The immune system is the body's defender．It identifies，tracks own，and destroys troublemakers before they can hurt the body可知我们的免疫系统的功能是破坏捣者为了不伤身体；故选C．
29．A．细节理解题．根据文章Yet they attack everything that is foreign to our bodies，such as germs，transplants，and even our own cells which have become abnormal，as in the case of cancer可知T细胞会检测移植细胞，癌细胞和健康细胞；故选A．
30．B．推理判断题．根据文章据第一段The immune system is the body's defender．It identifies，tracks own，and destroys troublemakers before they can hurt the body可知文章主要讲身体的免疫系统是如何工作的；故选B．
点评 考察学生的细节理解和推理判断能力，做细节理解题时一定要找到文章中的原句，和题干进行比较，再做出正确的选择．在做推理判断题不要以个人的主观想象代替文章的事实，要根据文章事实进行合乎逻辑的推理判断．
