11 ．某药物静脉注射经过 3 个半衰期，其体内药量为原来的 (       )

A ． 1/2                                                           B ． 1/4

C ． 1/8                                                           D ． 1/16

12 ．不属于中央室的是 (       )

A ．血液                                                         B ．心

C ．肝                                                            D ．肌肉

13 ．能反映单室模型静脉注射多剂量给药体内药物蓄积程度的是 (       )

A ． R ＝ 1/1-e^{-k τ}                                               B ． f_ss(n)=1-e^{-nk τ}

C ． DF=k τ                                                    D ． FI=(1-e^-k