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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 nonª²self 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 nonª²self and execute a misdirected immune attack.

¡¡¡¡[C] When a normally functioning immune system attacks a nonª²self 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 selfª²tolerance.

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

¡¡¡¡[A] the su