brain in intricacy.

　　[C] is enclosed by numerous sensitive cells.

　　[D] results in an effective communications network.

　　2. The principal task of the immune system is to _______________

　　[A] recognize and eliminate all foreign molecules that enter the body.

　　[B] remove all the substances that invade the body organisms.

　　[C] defend the body from the attacks of different viruses and bacteria.

　　[D] identify and specify all non�瞫elf molecules it encounters.

　　3. The remembering power of a person’s immune system is _______________

　　[A] mostly descended from his/her ancestors.

　　[B] partially passed down from his/her mother.

　　[C] mainly acquired through fighting against foreign cells.

　　[D] basically generated by its communications network.

　　4. Which of the following is NOT true according to the passage?

　　[A] A tissue transplanted from father to daughter would be less acceptable than that transplanted between twins.

　　[B] The immune system would never wrongly identify self as non�瞫elf and execute a misdirected immune attack.

　　[C] When a normally functioning immune system attacks a non�瞫elf molecule, the system will remember the specifics of the foreign body.

　　[D] The immune cells and other body cells can coexist peaceably in a state known as self�瞭olerance.

　　5. The main idea of the passage may be generalized as_______________

　　[A] the su