9．Can you imagine a classroom missing one thing that has long been considered a necessary part to reaing and writing？No notebooks，no textbooks，no test papers．Nor are there any pencils or pens，which always seem to run out of ink at the critical moment． A"paperless classroom"is what more and more schools are trying to realize．Students don't do any handwriting in this class．Instead，they use handsized，or speciallydesigned computers．The teacher downloads texts from Internet libraries and sends them to every student's personal computer． "Having computers also means that students can use the Web．They can look up information on any subject they're studying，from maths to social science．" High school teacher Judy Herrel in Florida，US，described how her class used the Web．"Using a book that's three or four years old is impossible，"she said． A paperless classroom is a big step towards reducing the waste of paper． "Think about the money and trees we could save with the computers，"she said． But，with all this technology，there's always the risk that the machines will break down．So，in case of a power failure or technical problem，paper textbooks are still widely available（可得到的）for these hitech students．
28．The underlined word"critical"in the first paragraph probably has the same meaning as"D"． A．worrying B．dangerous C．happy D．important 29．In a paperless classroom，what is a must？B A．A pen． B．A computer． C．Information． D．A pencil． 30．According to Judy Herrel，C． A．the Web can take the students everywhere B．the Web can take the place of teachers C．the Web is a better tool for information D．the Web is for downloading information 31．Which of the following is not supported by the writer's opinion？C A．The paperless classroom will be good for trees． B．There are some differences between the paperless studies and those in the usual way． C．Paper textbooks are no longer useful． D．Paperfree studies are popular with more and more schools．
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？
