43. How do trypanosomes withstand the attack of a host's immune system? (A) The molecular composition of their surface changes continually. (B) They reproduce so fast that they can compensate for the death rate caused by the immune system. (C) They live only in the cerebrospinal fluid, where the immune system can't reach them. (D) They specifically poison helper T cells. (E) All of the listed responses are correct.

45. B cells have antigen receptors that bind to antigens that are either freely dissolved or present on the surface of invading/foreign cells. T cells have antigen receptors that (A) bind only to antigens present on the surface of the invading/foreign cells. (B) bind to antigens that are either freely dissolved or present on the surface of invading/foreign cells. (C) bind only to freely dissolved antigens in the plasma. (D) are active only in lymph nodes. (E) bind to antigen fragments presented on major histocompatability complexes by host cells.

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