题目内容：

Harmful microbes (微生物) like bacteria (细菌), viruses (病毒) and other germs (病菌) are pathogens (病原体). They may enter your bodies and make you ill. The immune system (免疫系统) is the body’s defence (防卫) system that protects you from illness and disease caused by the pathogens.

The immune system is made up of non-specialized defences such as skin, tears and the acidic juice produced by the stomach, keeping you from the pathogens. It also has some highly specialized defences, which are different kinds of immune cells (细胞), grouped into phagocytes (噬菌细胞) and lymphocytes (淋巴细胞). Phagocytes are a type of white blood cell. They are swimming around in your blood stream, always on the lookout for antigens (抗原) —the pathogens that have entered your bodies. Whenever they see one, they will eat it. However, some antigens are hard to find and kill. Then lymphocytes, which are also white blood cells and the main types are B cells, T helper cells and T killer cells, will be the killers of the sneaky antigens. B cells, T helper and T killer cells work together to find and kill these antigens. B cells produce substances, called antibodies, which stick to the antigen. When that happens, it will tell the T helper cells to come over and either: 1. help the B cells kill the antigen, or 2. call the phagocytes or T killer cells to move in for the kill. Once a B cell or a T cell attacks an antigen, they create cells to “remember” it. Those “memory cells” hang out in your blood and if they see the same antigen again, they quickly recognize (识别) it so your immune system can act faster at killing it.

The immune system is more powerful than you probably imagine. Scientists from the University of Pennsylvania recently took immune cells from three patients with leukemia (白血病), then genetically changed them into “serial killer” cells to attack cancer cells. The study was small but the results were ground-breaking. The modified immune cells increased at least 1,000 times in the body and killed all the cancer cells. Therefore, more “memory cells” were created.

The immune system can be developed. Eating lean protein food (beef, beans) and food rich in vitamins A, C and E (sweet potatoes, carrots)，taking a 30-minute walk every day and reducing your stress levels, will help you achieve it.

1.The immune system can _________.

A. keep you from antibodies.    B. protect you against antigens.

C. make your bodies weak and sick.    D. help microbes enter your bodies.

2.How are the sneaky antigens found and killed

A. B cells produce antibodies to tell T helper and T killer cells.

B. B cells create “memory cells” to swim around in the blood.

C. Skin, tears, acidic juice and immune cells work together.

D. Phagocytes, B cells, T helper and T killer cells work together.

3.After a B cell or a T cell attacks an antigen, they create _________.

A. phagocytes    B. lymphocytes    C. memory cells    D. serial killer

4.The underlined word “it” in the last paragraph refers to _________.

A. Less antigens can be killed by the immune system

B. The immune system can be changed into the “serial killer”

C. White blood cells act less quickly in the immune system

D. The immune system can be made more powerful

5.This article is mainly about _________.

A. the types of white blood cells    B. an introduction to the immune system

C. a research report about human health    D. the cause of illness and disease